Not totally sure what you mean but, say you close or minimise a finder/application window, just clicking on the dock icon of that application will bring up a new window if it was closed or 'maximise' a minimised window.
Theres no keyboard shortcut because you would need to be in that app for the shortcut to work and so a shortcut would actually be more effort than just clicking an icon (which you need to do anyway to get into the app).
I think that makes sense. 🙂