You are most likely to find a trench at a divergent boundary between two plates.
*additional note
You don't have to but if you want to I recommend downloading this:
https://phet.colorado.edu/en/simulation/legacy/plate-tectonics
I'm currently in seventh grade and the assignments we are given in science is focused on earth and its layers. (because of schools closing ya know, online assignments and stuff, our teacher gave this helpful simulation sort of game)
Hope that helps! (it's basically a simulation of how plates form the way they do)
