No se entera de nada

[ROBINDESBOIS]

No se entera de nada, no sabe por donde le da el aire, no tiene ni idea significa que no entiende ni jota.
Are there any sayings in English ?
For example : Not to understand a fig ???

[pjt33]

He doesn't have a clue.

Si se trata más de falta de inteligencia que de falta de conocimiento:
He doesn't have two brain cells to rub together.

[Tomisimo]

I agree with pjt33,

He doesn't have a clue.
He's clueless.
He's out of it.
He's out of the loop.