It beats me. 難倒我了。
It beats me why he did not show up today.
我不明白他為什么今天沒來。
It beats me how he does his work so quickly.
我弄不懂他怎么能做得這么快。

關于困惑其他表達：
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緒變化弄得一頭霧水。
A bewildered look 一臉問號

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

Puzzle 謎，智力游戲；使困惑，使糊涂
What puzzles me is why some people are so moody.
讓我困惑的是為什么有些人這么喜怒無常。
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.
我不明白你為什么沒有出席昨天的會議。
Your absenteeism baffles me.
你的缺席讓我不解。
This question has baffled scientists for years.
這個問題已經困擾科學家們數年之久了。