YOU SAID:

I dont know about that one chief

INTO JAPANESE

私はその1人のチーフについて知りません

BACK INTO ENGLISH

I don't know about that one chief

INTO JAPANESE

あのチーフのことは知らない

BACK INTO ENGLISH

I don't know that chief

INTO JAPANESE

私はそのチーフを知りません

BACK INTO ENGLISH

I don't know that chief