Was Socratis wrong about this?

Socratis says he can know that he’s ignorant of something. But to “know” your ignorant of something would’nt you have to know it to know that? Otherwise how do you know? What’s your thoughts on this?

I know of mandarin Chinese. I do not know mandarin Chinese, and am therefore ignorant of the ‘content’.
Yes, you can only know that you are ignorant of something, the existence of which you are already aware, to some extent or another.

All I know is I don’t know…All I know is I don’t know nothing! (and that’s fine)

He probably meant that all he knew was that he didn’t know anything about moral essences. Socrates didn’t venture further than moral philosophy, and I seriously doubt that he thought he didn’t know he had hands.