Does Golurk's "Superpower" attack apply Resistance to the +20 damage it does to itself?
Yes, as long as Golurk is Fighting Type at the time of the attack, Resistance would be applied.
Superpower




x2
-20
Bubble BeamFlip a coin. If heads, your opponent's Active Pokémon is now Paralyzed.


SuperpowerYou may do 30 more damage. If you do, this Pokémon does 30 damage to itself.
Does Golurk's "Superpower" attack apply Resistance to the +20 damage it does to itself?
Yes, as long as Golurk is Fighting Type at the time of the attack, Resistance would be applied.