In tWoN the aggravated Harm isn't associated to any Pool. It don't shake down at the end of the Extended Conflict, but if I heal it by an appropriate Ability check to turn all aggravated Harm equal or under the check result into normal Harm, which also shakes the Harm down.

For only mechanical purposes: if the healed damage, after being shaken down, is still at level 4, which pool will receive malus dice?

I'm making an adaptation for Exalted. I like the aggravated Harm associated to a Pool. It can be reasonable associating aggravated to a Pool?

You know, that's a good question - the book is needlessly vague about it. Good to know that you're reading the text so close as to catch that :D

Aggravated Harm is associated with all Pools for the purposes of penalty dice in the case of Major Harm. When it is healed, the healer determines which Pool it transforms into based on what makes sense. Another way of doing it would be to have Aggravated Harm be differentiated normally between Pools as "Aggravated Vigour Harm" or such, which'll allow directing the Major Harm penalties and the healing more accurately - no big deal either way, use whatever tickles your aesthetics. I like the idea that Aggravated Harm is a "type of its own" because it allows me to just mark down an "A" on the Harm track instead of "V", "I" or "R" in the Harm type box.

What sort of aggravated Harm do you have in Exalted, by the way? I'm not sure I understand your last question, but if it is whether to associate Aggravated Harm into specific Pools at the time it's inflicted, I don't see why not - it's a matter of taste, no serious repercussions either way.

I've 3 Pools: Body, Mind, Essence.

I've Secrets that directly inflicts aggravated Harm, because an attack directly to my Essence inflict Aggravated Harm in Essence or that inflict tremendous wounds to my Body, ecc.

I like, for my adaptation, establish the Pool for aggrataved Harm. I don't see problems about that, but the question is dutiful. ^^