Happy Monday!
Our idiom today is you've got me.
This means you don't know the answer to the question.
Example 1
A. What is my sister's name?
B. Hmm, you've got me. (Can also be said as "you got me")
Example 2
A. Do you know who won the Gold metal in the 100 meters, at the 1936 Berlin Olympics?
B. That's a good question. I don't know. You've got me.