낫 놓고 기역자도 모른다. (Nat nokko kiyuk-ja do morun-da.)
That's a Korean proverb that translates to:
One doesn’t know the "ㄱ" (kiyuk - a Korean alphabet) even when looking at a sickle.
It reminded me of my mother saying that someone "متايعرف الواو من عصا الطبال", so ignorant he can not tell the letter "waw" from a drum stick.