Just been trying to implement this with no joy 
No matter what I setup, custom event or an interface event, it just will not trigger within the event graph of my widget blueprint.
I’ve tried watching your video several times and whilst you clearly know what you’re doing, you jump around a lot and far too quickly for me I’m afraid.
Probably best if I show precisely what I have working already:
(top image is my character BP, bottom 2 images are my widget BP event graph and function)
This does the desired effect of updating an on screen textblock to show how many times the RingHit event has triggered (which is fired by the player overlapping any pickup blueprint in the world).
As I mentioned though, this setup still has the widget checking this value every Tick which is what I want to avoid.
I’ve simplified this a lot for the sake of the screenshots, but I really need to get my head around how it can be handled in more complex cases.
Thanks for any extra help you can give.