Is what the friend did, touching his sister's private parts without penetration or ejaculation, considered zina (illicit sexual intercourse) that necessitates the death penalty? And is it permissible for him to travel to Saudi Arabia to confess and receive the punishment of lashing if his act does not necessitate the death penalty, so that he may expiate his sin and regain his humility, knowing that he does not currently feel remorse?

The adultery that necessitates a legal punishment (Hadd) is the penetration of the male organ into the female organ. Anything less than that necessitates a discretionary punishment (Ta'zir). It is obligatory for anyone who commits these sins to conceal themselves and not inform anyone, and to repent to Allah with a sincere repentance by abandoning the sin, regretting it, and resolving never to return to it. The greatest pillar of repentance is regret.