Does Marowak's "Bodyguard" Ability prevent me from revealing my hand from an opponent's Trevenant's "Poltergeist" attack?
Yes, it does.
PoltergeistBodyguard




x2
Confuse RayYour opponent's Active Pokémon is now Confused.

PoltergeistYour opponent reveals their hand. This attack does 40 damage for each Trainer card you find there.
Does Marowak's "Bodyguard" Ability prevent me from revealing my hand from an opponent's Trevenant's "Poltergeist" attack?
Yes, it does.