Instead of testing HitActor, grab HitComponent and check if it == TopBox (or more likely, one of it’s collision boxes).
Doing this you should be able to figure out which drawer you hit, and send the execution to that specific drawer (or to the desk, telling it which drawer was hit).
You might need to use a multi line trace if the desk collision will get in the way.
But then the line trace might also go through to drawers underneath as well, so you’ll need to figure out how to handle that (probably just grab the first drawer component that was hit, from the trace array)