One of Superman's coolest aspects is that while we know that he can use Martial Arts, he opts never to use it even when fighting against villains nearly as strong as him. It feels like Superman spoke that "I don't need to use martial arts to defeat you, I only need to use my powers," and to be honest, I think he never needs them. I mean, Superman's full power punch is already destructive enough to guarantee a knockout blow or killing blow for some, so what use of martial arts for people like him.