That's not clear. 我不清楚。
I can't see your point. 我不明白你在说什么。
I'm not sure what you mean.我不明白你的意思。
I don't have any idea what's going on. 我压根不知道是怎么回事。
It's over my head. 太难懂了。
It's beyond me. 我完全不能理解。
