This trophy is called "Y-You Got It!
" and it requires a fellow Survivor to mark an item and then you mark the same item.
The description for the trophy doesn't really give a great indicator of how to unlock it.
To unlock this, a Survivor needs to mark an item using L1. Once they have marked an item, then you must also mark the same exact item using L1. You'll then unlock the trophy.
Once unlocked, the trophy name makes sense. Basically it's someone stunned you're marking the item they just marked.
Here's the video that the PS5 recorded when I unlocked it: