Zoroark GX's "Trickster GX" attack allows you to copy an attack from any of your opponent's Pokemon. Does this allow you to copy an opponent's GX attack or not? If so, what if your opponent has already used up their GX attack for the game?

Yes, Trickster GX can copy an opponent's GX attack, even if the opponent has already used up their GX attack for the game. It does not count as using 2 GX attacks.

Relevant cards

SM35_77A