Some of these seem fairly obvious, others less so. Since, however, Pax rules are far from easy to understand, I've chosen to reprint all of them (edited mostly for ease of reading).

Q: Can a state/dominion be part of a codominion?
GC: Well, the rules aren't clear on the subject, but I'd say 'no'.

Q: The rules say "Areas use their Combat Strength for defense exclusively.". Is there not an exception, during a Chinese rebellion, when an area can add its strength to attacking Chinese armies?
GC: Yes.

Q: "An Army Unit cannot move from a Sea Zone to a Coastal Area containing an opposing Naval Unit, and vice versa." Similarly, for blockades of supply. Presumably, this restriction applies only if the Naval Unit is on the appropriate coast.
GC: True.

Q: Does the US player have a Casus Belli against a player that places a Control marker in Alaska (assuming that the US has lost his)? That Area does begin the game with a Control marker, but perhaps the exception was intended only for Canada, Guiana, and Newfoundland?
GC: Yes, sure; the Monroe Doctrine should include Alaska.

Q: Is it a general rule that military units can end a phase only in home or controlled areas (or sea zones for navies)?
GC: Yes.

Q: Is garrisoning mandatory if units are available?
GC: It is, yes.

Q: Suppose that a treaty is signed at a time other than the Negotiation phase or the CoE phase. If the treaty specifies downgrading of status markers, is it the case that this can happen only if otherwise allowed by the rules (e.g., removal of an influence during the movement phase)?
GC: Yes.

Q: Would such a downgrade/removal cause an ETI increase?
GC: I would guess not, given that the treaty might be secret and a removal outside of Negotiation/CoE is already allowed and not subject to ETI increase. Such an aspect of a treaty couldn't be secret, since it would be visible to other players on the game-map. If it's voluntary and no Casus Belli existed, I don't think it would increase ETI.

Q: Under what circumstances does removing Interest/Influence markers during the movement phase not increase ETI?
GC: If you have an Interest or Influence marker in an area with other Influence and Interest markers only. In this case, you don't have a Casus Belli, so there's no obvious cause of tensions and removing the marker isn't a retreat in the face of another power.

Q: Does the removal or downgrading of minor-power status markers increase European tension?
GC: Yes.

Q: Since Bulgaria gains a Mediterranean coast after the second Balkan war, is the overland route between Anatolia and Greece lost? Or are these areas assumed to remain adjacent through the Aegean islands?
GC: The latter.

Q: CB's based on status conflict must be resolved by negotiation, CoE, or war. Other CB's can be territorial (US in North America or Britain in or around India) or based on treaty (including pledges to Minor Powers). It is stated that these must be acted on in the turn they transpire or be waived permanently. Am I correct in that the permanence of this waiver applies to specific instances only? For example, suppose Italy establishes a Protectorate in Baluchistan and Britain waives the CB.
Does Britain again have CB if
- Italy later gets control of Burma (the waiver applied only to Baluchistan)
GC: Yes.
- Germany later gets control of Burma (the waiver applied only to Italy in Baluchistan)
GC: Yes.
- Germany later shares control of Baluchistan with Italy (the waiver applied only to Italy, which got not rights to transfer it under codominion)
GC: Yes.
- Germany later gets control of Baluchistan from Italy through negotiation (the waiver applied only to Italy)
GC: I'd say not: the CB applies "each time another player PLACES a control marker," and in this case ownership of the control marker is being changed; no new control marker is being placed.
- Germany later gets control of Baluchistan after Italy has lost it (the waiver applied only to Italy) GC: Yes.
- Italy later gets control of Baluchistan again, having previously lost it (the waiver applied only for that one placing of a control marker)
GC: Yes.

Q: Your rules clarification states that a war with the Ottomans can be a Great War only if (1) 4 or more European powers are involved and (2) the Ottomans have a Great-Power ally. Can one generalize this as follows: a war is a Great War if 4 or more European powers are involved and there are Great Powers on both sides of the war?
GC: Yes, except in a four-player game (see top of p 22).

Q: This would mean that a Chinese rebellion can never be a Great War. I couldn't find this stated explicitly in the rules, although I may have missed it. But the historical notes clearly state that there was a pre-1914 Chinese rebellion that included 4 or more European powers, but I assume that this is not the Great War that ended the "game" in real life. Can a Chinese rebellion be a Great War?
GC: No, in a Chinese rebellion, it's always the powers against the Chinese.

Q: Suppose that there is a war that included 4 or more European powers on one side but no European Great Powers on the other side. Is this a Great War if
a) the other side is a minor power with no Great-Power ally?
GC: No.
b) the other side includes the US and/or Japan?
GC: An unlikely scenario--Europe united--but I suppose it would be a Great War.

Q: Can a communication link be traced through areas with unestablished control markers? The rules say "Areas under the player's control".
GC: No, it must be an established marker.

Q: What happens if the game ends in the middle of a war (as seems likely) either because the ETI reaches 100 or because a fourth European power enters the war? Specifically, which status markers are used for final victory-point determination? The rules say that status markers are not removed, added, etc. as a result of conquest *during* a war, only when it is resolved. So, since a game-ending war is never resolved, this seems to suggest that victory-point determination would be based on the status quo before the war began. In a sense, this makes some sense, the war going on is the Great War and it might make sense to evaluate conditions as they existed before the Great War (the game is supposed to be up to but not including the Great War). Do you agree?
GC: Yes... status quo ante, as it were.

Q: Would a naval unit in Egypt or Anatolia blockade both coasts?
GC: Yes, a naval unit here blockades both coasts.

Q: I assume that the same would hold for Central America or Panama if a canal exists there.
GC: Yes.

Q: Am I correct that a player cannot block these during war if it has a control marker in the area but the area has been conquered?
GC: Yes

Q: Can the conquering player then block?
GC: Yes, whoever is in effective control.

Q: What there are forces of both sides currently in the area and the controlling player is not a neutral? Open to all (as if it were a codominion)? Closed to all? Open only to the original controlling player's side?
GC: Not sure how that would happen; surely one side or the other will retreat or be eliminated in combat? If there are forces from both sides because one side has moved units into the province this Maneuver Phase and combat has not yet been resolved, then the "owner" of the province is still the last player to control it, and he can block movement through the canal/straits.

Q: Can a player benefit (gain victory points) from a one-sided defensive treaty (e.g., Britain agrees to defend Japan, but not vice versa)?
GC: Yes, but only the side that benefits can gain points, e.g., France and Russia both normally gain points for a treaty of mutual defense, but if they have a "France will defend Russia but not vice versa" treaty, I would rule that only Russia gains victory points from the treaty.

Q: More to the point, I have seen a quite a variety of "defensive" treaties used in various PBEM games. Would either of these be sufficient to gain victory points as specified in the rules?
Q1: France and Britain agree to a mutual defense pact. If either is attacked and calls for aid, the other will render it by declaring war on the attacker. However, if the attacked party does not call for aide, no declaration of war is required (perhaps even no CB comes to exist).
GC: Sure.
Q2: France and Britain agree to a mutual defense pact. If either is attacked, the other will render aid by declaring war on the attacker. However, this clause is void if such a declaration would trigger a Great War.
GC: I don't have any problems with this, either. It's 2 points a turn; perhaps you might rule that, on the final turn, it doesn't really qualify as a defensive treaty, because the imminence of the Great War renders it ineffective, but up until then it is a genuine defensive treaty.

Q: Given that only one player has to put down Unrest, how do you (the GM) decide who does so if multiple players are present with troops in an area?
GC: Units can only be there in order to establish a control marker. The question is moot; the "first" attacker suppresses the unrest through colonial combat, but the other attackers must also engage in colonial combat to establish their control markers.

Q: Spoils cannot be taking at the end of an Ottoman war. That is, if the war was over Anatolia, Tripoli and Quwait stay under Ottoman control at the end of the war. Other territories (originally controlled by other players) can change hands in the war, as usual. But what about Anatolia itself (in this case)? Suppose the Turks lose the war. Can the power that originally took control of Anatolia set up a Codominion there with its allies after the war? If so, do those allies need to pay for their markers for the Codominion (if they're set up right at the end of the war)?
GC: The war will be triggered only if someone sets up a control marker in Anatolia, since that's the trigger for an Ottoman war. (I assume this will happen, as it's too good an opportunity to pass up.) The normal "end of war" rules apply; should the anti-Ottomans win, then there is a protectorate or possession marker in Anatolia, and the owner of that can put any legal Status marker in that area at no cost.
Q(MO): Regarding the previous question, why can the owner put in any legal status marker?
GC: Per Negotiation and Ending a War, p. 24, "The victorious players can, by mutual agreement, put any legal Status markers in each of the Areas conquered from the defeated Alliance... at no cost in (pounds)". True, Anatolia isn't, in this case, quite an "area conquered from the defeated alliance," but close enough for rock and roll.

Q: If four European countries end up in an Ottoman war, not all on the same side, a Great War breaks out. According to the rules, only the Ottomans declare war; other countries merely say if they are joining one side or another, but no DoW is required. Moreover, in a PBM game, these players might all join the war simultaneously. The question, which player(s) (if any) get the 3x Great War Penalty?
GC: Neither the existing rules nor my PBM rules deal with the problem of simultaneous movement and the difficulty in determining the "first" and "last" declarer for Great War penalty purposes. Should the gamemaster already have house rules to cover that situation, they should apply, and nothing I say should over-ride them. I would rule that anyone who places a control marker in Anatolia in the first instance is a "first" power--because even though the Ottomans are declaring war "first," in some sense, it's their aggressive move against the Turks that's starting the Great War. Players who wish to aid the Ottomans must declare before players wishing to support the Ottoman enemies; even if declarations are performed simultaneously, I would use this to establish some kind of sequence. So: control marker placers; Ottoman allies; other powers opposing the Ottomans. We can't establish a sequence of declarations within each of these three groups, so I'd consider all control marker placers "first declarers;" if the fourth power shows up among Ottoman allies, I'd consider all Ottoman allies "last declarers;" and if the fourth power doesn't show up until the third group, I'd consider all of THEM last powers.

Q(MO):In the errata, there exists an alternate rule that lets the Ottomans take areas that border them and go into Unrest. This being the case, it is now possible for powers to gain CBs against the Ottomans (i.e GB has an Influence in Persia, doesn't put down the Unrest, the Ottomans invade). It has been the contention of several players that since this is a CB against the Ottomans, powers should be able to DoW the Ottmans and take all their territory, as in wars with any minor power. Of course, the Ottoman rules in the main book strictly rule out any reparations, but those rules only deal with the Ottomans holding CBs (effectively) against players rather than vice versa. I was just curious about your thoughts on this.
GC: I'd treat it like another Ottoman War, e.g., you can only take areas under dispute... Unlike other minor powers, the Ottoman's don't have a safe, unconquerable home territory. And in reality, dismembering the Ottomans entirely would take a major congress; e.g., if anyone tried to take the Straits, the British would go nuts.

Q(MO): Should people be able to draw on Merchant Fleets for Coaling Rights as well, or is this intentionally left out?
GC: No, merchant fleets don't work for coaling rights. The cruise range of a capital ship from the period was fairly limited; they literally needed to recoal pretty frequently. The Russian fleet's ill-fated trip from the Baltic to the Pacific during the Russo-Japanese War was, at times, in jeopardy because of the difficulty of finding ports where they could recoal along the way. I don't know of any instance of a ship being refueled at sea at the time.

Q(MO): Under surrendered Units, it says Units will surrender when "out of supply or unable to draw coaling rights". From this I'd have to gather Naval units must be checked for surrender, even though except for that line only Army Units (and Controls, based on your errata) are ever mentioned as being checked for surrender. Is this correct?
GC: Yes, naval units can surrender.

Q(MO):For a Canal Area, does a Line of Supply run through it (and hence is cuttable)? The rules specify that powers can't _move_ through an enemy-Controlled Canal, but supply is not addressed.
GC: Supply =would= be cut if a Canal Area falls into enemy hands. It remains open if the Canal is in neutral hands, regardless of the wishes of the controlling player (if any).