case: Is my opponents turn and he has him Pokemon poisoned, he KO my Poke and get Koed by poison. Who is the first player in put an active Pokemon me or my opponent?
You do.
The two KOs happen at totally different times.
Your Pokemon is KOd during his turn by his Pokemon's attack.
You replace your Active as the last thing done before the turn ends.
His Pokemon is not KO'd until between his turn and your turn, after you have replaced your Pokemon.