ἐπεὶ τίνα οἴει ἀπαρνήσεσθαι μὴ οὐχὶ καὶ αὐτὸν ἐπίστασθαι τὰ δίκαια καὶ ἄλλους διδάξειν
since who do you think will deny that he does not know what justice is and that he will not teach it to others? Is my translation correct?
No, it’s the opposite: “who do you think will deny that he knows … ?” i.e. “will say that he doesn’t know …”? The μη ου, with its “sympathetic” ου, is due to the negative sense inherent in απαρνήσεσθαι.
And note the καὶ αὐτὸν: “both that he himself knows and …”