From your description I don't fully understand what you're trying to do, but here's a couple things that hopefully will help.
1. In the `Widget Code` field of the Widget Content Type, you can reference the values of any of the other fields of the Widget Content Type using the ${fieldVarName} notation. For an example, look at the Widget content type in the starter/demo site (the actual VTL code is in the /application/vtl/widgets/you-tube/you-tube.vtl file, but look at the `Widget Code` field in the YouTube content type to see where that's used in the content type).
2. But when you create an instance of the Widget content type you're creating a content item, not a content type. And from your screen shot (which is showing the _content_ editing screen, not the _Content Type_ editing screen) it looks like you're trying to access the value of a field in that content item from another field in that content type, which doesn't work. The exception is if you create a custom field (in the Widget Content Type, not in the content item) and use js/dojo code to get the value of another field; but that code is still all in the widget Content Type, not in the widget content items.
So in short, any code that accesses other fields has to exist in the widget Content Type, not in the widget content items.