An interesting paradox

A friend of mine posted the below paradox on his wall.

XX knows that he does not know what else he needs to know

My reply was:

Do you know what you don't know?

You cannot don't know and know "you don't need to know" at the same time. Or perhaps you can know "you don't need to know" but do not know what's that thing you don't need to know?

After I finished typing my reply, I ended up confusing myself!