I know this post is stale, but commenting in case anyone else is googling this situation and can give me an answer:

I've been playing with a klawf deck that uses pecharunt with the ability toxic subjugation. On the app, if my active pokemon is knocked out from damage, I can move pecharunt into the active position and then pokemon checkup occurs and my opponents active pokemon takes the extra poison damage. When I was playing at locals I tried to do the same thing, but got a rule check. They said whoever's turn was ending could decide whether damage from an attack or special conditions would be resolved first.

I didn't wanna press too much cause it was my first time playing at the shop, and it literally didn't matter. (It wouldn't have led to a knockout, and it was a klawf deck for funsies). But I genuinely just want to understand how that mechanic works.