How many power does a Blue Sentinel equipped with a Skyfall of Areion generate on a conquer?

2 [A] (any-domain power), added at the start of your next Main Phase — assuming nothing else modifies it.

Skyfall of Areion doesn't replace Blue Sentinel's "When I hold" ability; it makes that ability also count as a conquer effect, so it now triggers when Blue Sentinel conquers. Because the ability is still a hold effect, Blue Sentinel's own passive ("Your hold effects for holding here trigger an additional time") applies to it, so you get two instances of "[Add] [A] at the start of your next Main Phase."

This is the mirror image of the documented Red Brambleback + Trinity Force + Skyfall line (your conquer-doubler applied to a hold effect that Skyfall converted into a conquer effect — FAQ #9537), and it follows Skyfall's general function that it adds trigger timing rather than replacing or duplicating instances (FAQ #5622, #288).

Two caveats: Skyfall grants a trigger, not an extra trigger — it's one trigger doubled, not two triggers from being "both" a hold and conquer effect. And this is Blue Sentinel's own [Add] ability, so nothing here changes your point total.