他正在和老师在办公室里讨论数学的英语

He is discussing the math with his teacher in the office.
你想翻译的是讨论数学吧～
数学是math.如果你要说的是英语，就改成English

He is discussing the English of math with the teacher in the office.

he is talking to his teacher about English and math in the office

He is talking with the teacher about math in the office.