noun
knowing look; know-it-all expression
Describes a facial expression or attitude that suggests one knows everything, often with a slightly negative or ironic nuance.
彼は物知り顔で説明を始めた。
He started explaining with a knowing look.
物知り顔でうなずくだけでは、本当に
Just nodding with a know-it-all expression doesn't tell me whether you really understand.