I accidentally restored a set of files (around 15-20 in total) from the trash, instead of deleting them (sic). Is there a way to undo this process or to find which files were restored to which directory, so that I can then delete those unnecessary files?
Not that I am aware of. Unfortunately, the .trashes file stores the location of the file until you either erase it or restore it. You're probably not going to find an easier way to do it other than to find the files and erase them again. Doing ctrl+z could have solved your issue the moment it happened, but it's probably too late for that.