I replaced my rear hub, but I'm not sure about how to attach the derailleur
Compare @mike 's photo with your hanger.   Yours does not show a bolt head.  Mike's does, and there's a specially-shaped nut on the other side.  



This semirounded nut is supposed to slide up the dropout, and acts as one anchor.  Your wheel axle acts as the other, to stop the derailleur rotating around.

Good news is these generic claw hangers are cheap, so buy the whole unit and you'll be able to fit the derailleur.

Note - you may need to file the backside of the rounded nut to get chain clearance in the smallest cog.