To unlock the I got the Poison... trophy in WWE 2K19 you need to select a superstar (or edit a wrestler's abilities before the match starts) so that the red Payback ability is Poison Mist and then execute it on an A.I. opponent.
Now you need to get pummelled enough to fill both the red and the yellow circles underneath the wrestler's name. Wait for an opening in which the red circle flashes which means you can use the ability. Hold R1 and press L1 to activate, and then you have a limited window to press Triangle and spray the poison mist. You'll know you've done it if a green spray ends up in the opponents face and they stagger.
Once you have pulled off the move the trophy will unlock. Here's a video guide from Oddfellows Gaming; it's the same steps for the PlayStation trophy too: