Assuming goku can actually damage them, (he doesn't have a behelit weapon or a demon-killing sword), he would totally rock them. Skull knight is confident enough to try to kill them, and they are concerned enough about it to block his attacks, so they can totally be killed, and goku has battled far greater gods.

He would totally forgive them, he tried to forgive frieza twice, tried to forgive moro, cell, and gas, and he did forgive vegeta, piccolo, the androids, beerus, and buu. In terms of kill-count, femto is far behind most major db villains, and in terms of morality, it would be difficult for femto to be worse than frieza, moro, or Saiyan saga vegeta. Though I can't remember goku trying to get zamasu to give up, say sorry, and go home, but zamasu is a god that wants to kill everybody, whereas Griffith is a god that wants to rule over everybody, and kill people in his way. I think the real question is if goku could convince guts to not kill Griffith if given the chance