When does Goku use dragon fist?

Answer 1

Gohan probably learned the Kamehameha in the Hyperbolic Time Chamber from Goku, when they trained together for the Cell Games.

There is a scene in the anime where Gohan performs the Masenko during the Saiyan saga, but shouts "Kamehameha", but this was an error on the part of Toei Animation.

Answer 2

in DBGT when he is fighting Omega Shenron... i think so but in Dragon ball he used it to kill king piccolo. but i am not sure if he did for king piccolo, it was some kind of fist

Answer 3

when he was fighting broly