。
I agree with him on that point.
Literal
I [topic-は] that point [on-で] he [with-と] opinion [subject-が] match.
意見が合う literally 'opinions match' is the standard way to say 'to agree with' — opinions (意見) are the grammatical subject of 合う ('to fit, match'). 彼と marks him as the co-participant. その点で uses で for 'at/on that point' — a metaphorical location.