一窍不通

一窍不通 [yī qiào bù tōng]

[Interpretation] Trouble: hole, referring to the mind's orifices. There is no one hole that is through. Metaphorically, there is no understanding at all.

[Source] Yuan - Zhang Guobao 《罗李郎大闹相国寺》："Ah; this old man doesn't know a single trick."