YOU SAID:

i dont understand his name

INTO JAPANESE

彼の名前を理解していません。

BACK INTO ENGLISH

His name does not understand.

INTO JAPANESE

彼の名前は理解していません。

BACK INTO ENGLISH

I do not understand his name.

INTO JAPANESE

私は彼の名前を理解していない。

BACK INTO ENGLISH

I do not understand his name.