I used Reference Viewer. This is how I found it it is being referenced in GA_AbilityWithWidget.
I can’t understand where the value is populated. As we can see in the image, the details panel for the variable value is empty.
GA_AbilityWithWidget is just an empty parent class. In addition to the Class Defaults panel explained before, make sure to check "show inherit variables inside any GA blueprints derived from GA_AbilityWithWidget. You’ll get “Widget Classes”.