At the end of my turn, both players' Active Pokemon are Poisoned. During Pokemon Checkup my opponent's poisoned Pokemon gets KO'd, and they bring up a Pecharunt with "Toxic Subjugation" Ability. Does my Active Pokemon then receive additional damage counters for poison placed on it?
Both Poisoned Pokemon receive damage counters during Pokemon Checkup, then you check to see if any Pokemon are Knocked Out. A new Active Pokemon is promoted after the check for Special Conditions. So when Pecharunt is promoted Pokemon Checkup is already over and Toxic Subjugation would not apply.
Toxic Subjugation