YOU SAID:

I cannot understand what he is thinking

INTO JAPANESE

彼が何を考えているのか理解できない

BACK INTO ENGLISH

I can't understand what he's thinking

INTO JAPANESE

彼の考えが理解できない

BACK INTO ENGLISH

I can't understand his idea

INTO JAPANESE

彼の考えが理解できない

BACK INTO ENGLISH

I can't understand his idea