Is stoning and repentance incumbent upon one who enjoyed a woman unlawfully without penetration?

What your friend did is a grave sin, and he must repent to Allah for it and multiply his good deeds, so that Allah may perhaps expiate his evil deeds, for Allah Almighty says: (Indeed, good deeds do away with evil deeds. That is a reminder for those who remember.) [Hud 11:114]. Stoning or flogging is only for penetration of the male organ into the female organ. Anything else warrants a different punishment according to the degree of the forbidden act. He is not obliged to confess what he did to a judge; rather, repentance between him and Allah suffices.