And a second Answer for good Messure. The more “Proper way” of doing it.
Make a Actor (or other Base Class) Variable in your Widget BP and expose it on Spawn. Let your Individual NPC´s/Players Create the Health Widget (everyone gets one no need for a Massive one who Handles everyone) pass “self” to the Widget. Now your Health Widget knows from who to pull Data from (you simply pass it along).
Preferably you would have a common Base Class for your Character, NPC´s etc or a simple Component that holds Health and other Data you might want. Just pass along where you want to get the Data from.
Good Luck and take a smart approach =)