。
Do you know anything about his background?
Literal
His previous-existence [about-については] something know [honorific-ご存じですか]?
前身 (ぜんしん, 'previous position, background, former incarnation') asks about what came before — his earlier career, origins, or past life. ご存じですか is the keigo form of 知っていますか ('do you know?'). The question is formal and somewhat investigative in tone.