FWIW it does show the note/title on hover of a bookmark reminder notification, but not on hover of the bookmark in the menu you show in your post, so I think that could be one quick fix for this that would be helpful.
It is tricky. I think it would be much more useful to also show the title/note in the notification/bookmarks quick menu alongside the topic title but that would probably make everything way too long. I’ve always thought it was a bit awkward that we aren’t really showing the note anywhere but on hover and in the user bookmark list.