Is there a way to see what widgets are being used on pages?

From an admin perspective, it used to be easier in v11 with the "Bulk Replace Widget" functionality, but it changed in v12. I haven't ended up trying it, but there's an explanation on  Bulk Replace Widget in v12 : 

Widget replacement still exists but the entry point is a little different in 12+:

1. Go to Administration > Interface > Widgets (not widget studio)
2. Find the widget you want to replace in the list and select it.
3. Click "Replacement" to start the replacement process.

Here are a few more references I found too (from my comment here  RE: Find where a widget is used) :

•  how to identify custom widgets that are not being used in the community? 
•  RE: Forums - Delete Post -- Is this deprecated in 12.1?