Your question is a little difficult to follow. You've got a property on a form and you're trying to read it back off a window? Clearly that can't work. You should just be able to grab the form (probably using component query) and read it off.
Alternatively, perhaps that isn't what you meant. Perhaps you've just got a scoping issue? Without seeing your code it's difficult to say exactly how to fix it but you probably need to include a scope config somewhere.