Just wanted to make sure, but his ability is only for HIS ship right? not the whole fleet?

Correct. Whenever someone says "You" they actually mean "THIS SHIP"

Which is why the Global Effects (Fleet commanders) usually specify "A Friendly Ship"

So is Dodonava (or how ever it is spelled) for a fleet or just for when your flag ship does crit?

Dodonna triggers any time an enemy ship is dealt a face up card--even from asteroids, minefields, etc.

In fact, you'll notice that the only commander with the word "you" on it is Tarkin, and it's in a context where it obviously refers to the player ("you may choose 1 command"). That's because they all (so far) apply to every ship across your fleet without respect to which one the commander is riding on.