- Does using Lugia GX's "Lost Purge GX" attack count as KO'ing a Pokemon?
- No, it does not. You are moving the opponent's Active Pokemon and all cards attached to the Lost Zone, and since it does not count as a KO you don't get to take any prizes for it.
Source:
Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)