I find myself frequently duplicating various notes I have for various reasons. Bear supports a “duplicate” feature from the menu, but there is no keyboard shortcut for this functionality. My original expectation was this would work the way things such as the Finder work. If I want to duplicate a file on my desktop I can cmd-c/cmd-v to copy/paste it from one place to another. It would be nice if Bear supported that for notes. There is support for cmd-c/copy(ing) a notes’s contents in the note list (i.e. I can paste that markdown into another app). But, there is no cmd-v/paste support from within Bear itself to essentially create a new note with the same contents (i.e. duplicate the note). Another possible option is to just add a keyboard shortcut for the duplicate functionality, but I personally think the copy/paste approach is more idiomatic.
You can assign keyboard shortcut in your mac System Settings→Keyboards→Applications→Bear (for Duplicate or any other menu item), if I understand correctly your post.