It beats me. 难倒我了。
It beats me why he did not show up today.
我不明白他为什么今天没来。
It beats me how he does his work so quickly.
我弄不懂他怎么能做得这么快。

关于困惑其他表达：
Bewilder 使困惑、使疑惑
Men are often bewildered by a woman's sudden change of mood.
男人常常被女人突然的情绪变化弄得一头雾水。
A bewildered look 一脸问号

Perplex 使困惑，使疑惑
I'm perplexed by some people's high volatility of emotion.
我被有些人的情绪起伏之大弄得很疑惑。

Puzzle 谜，智力游戏；使困惑，使糊涂
What puzzles me is why some people are so moody.
让我困惑的是为什么有些人这么喜怒无常。
Puzzle over/about sth
to think hard about sth in order to understand it
苦苦思索以求弄明白某件事

Baffle 使困惑，使糊涂
I'm baffled why you did not attend the meeting yesterday.
我不明白你为什么没有出席昨天的会议。
Your absenteeism baffles me.
你的缺席让我不解。
This question has baffled scientists for years.
这个问题已经困扰科学家们数年之久了。