On Evolve - Select an enemy follower on the field. Reveal the top card of your deck and deal damage equal to its cost to the selected follower.
QCan I choose which enemy follower to deal damage to after revealing the top card of my deck?
ANo, you can't. If an ability requires you to select a target, you must do so before resolving the rest of the ability. Therefore, you must select an enemy follower before revealing the top card of your deck.