~냐 and ~느냐 are a common casual question form, so 하냐 means "Are you doing?" or "Do you do?". They are not full expressions by themselves. Here are some realistic expressions: - 너 뭐 하냐?: What are you doing? What are you up to? - 이건 어떻게 하냐?: What do you do with this? - 이제 어떡하냐?: What do we do now?

하느냐 is an antique expression of 하냐. It is not dead yet, but still alive within the old generation. Grammarians say that nowadays 하느냐 is on the way of being integrated into 하냐.