Is there a way to know which question/answer is linked to a badge on my own profile?
I just won a necromancer badge and I don't know from which one.
Click on the badge on your profile page. It will list the question(s/answer(s)) for which you've received that badge.
Note: (I believe) this only works for badges that are tied to specific posts, but it doesn't seem to work for all of them (doesn't seem to work for Disciplined, but it could be related to deleting the post/having-vs-not-having 19k rep).
Couldn't you look at your reputation history to see which answer recently reached the 5 upvote mark?
Not a perfect solution, but you should be able to find which answer earned you the badge.
There is no simple method other than doing some detective work on your own. This is definitely something that would be nice, IMHO.