I think it is कमीज़ and not क़मीज़
If you ever want to write Hindi as "Urdu" (i.e. in Arabic script), it will help to distinguish k and q wherever possible.
I thought it was यह when direct but इस when oblique, so why isn't this इस क़मीज़ पहनो?
It is not in oblique case in this sentence but rather in direct case since it is a direct object.