If my opponent used Hisuian Zoroark's "Doom Curse" attack to KO my active Great Tusk ex at the end of my next turn, would I still have to discard the top 5 cards of my deck for Great Tusk ex's "Quaking Demolition" Ability or not?

If there's an effect that KO's Great Tusk ex at the end of the turn Quaking Demolition will still trigger. All end-of-turn effects process first, then you check for any KO's afterward.

Relevant cards

SV45_53

SWSH11_76