I have tried breeding my Noctowl with my Ditto but it didn't work.
Take your Noctowl to a Move Relearner (like the guy in Pastoria City), you can learn the move there. I think in HG & SS it's in Blackthorn City.
Go to the move tutor in Blackthorn City and bring a Heart Scale so you can re- learn it on Noctowl. Breed a Female Noctowl with a Male Pidgey to get Sky Attack on your Hoothoot.