He was in the ANBU and had a lot of natural talent. He would definitely have been helped by his father and Shisui with his sharingan and other clan tech. Other than that he probably he mostly did it himself and maybe Danzo helped him. It is actually possible that Obito might have taught him some kinjutsus that he learned from Madara given that Itachi was still technically just 13 when he joined Akatsuki. But still, what training do you really need when you have a Mangekyou Sharingan. Sasuke has had zero training I think since he killed Orochimaru and he has gone from High Jounin level to High Kage level, Amaterasu-ing every ant that crosses his way. Uchiha power seems more to do with feelings than training.