오~ 그렇게 다 아는 사람이 사는 게 겨우 그 정도야? (It sounds like a rhetorical question of sarcasm)
=> Ah, so a guy who knows so much is living like that (in such poor amenities)?
=> Ah, so a know-it-all like him can't afford any more than what he has? (Yeah, right, it makes a lot of sense!)
"사는 게" (사는 것이) is a loose term for how someone is living (in terms of amenities, wealth, etc).
"겨우 그 정도야" is literally "is (disappointingly) no better than that", meaning it is underwhelming.