He stands on his back two legs, takes both paws and grabs the door knob and tries to turn it. If the door isnt closed that well, i.e somewhat ajar, he can actually open it. The last black cat I had that I inherited from my uncle did the same thing. He’ll also “knock” if he can’t get through a door. And by “knock” I mean he’ll find the nearest loose bit of wood or paneling or something that he can grab hold of, pull it a little then let go so it snaps back and makes a fairly loud noise.