[Idiom] which one though?

[jeehae93217]

Situation

A person made a mistake and there is a list of files.
He doesn't know which file is wrong and he need to find out in order to fix the file.
in this situation, he said "which one though?"

Why he said though in the end of the sentence?
I don't understand the role of though.

 

[emsr2d2]

Please give us the entire dialogue. I can think of a context in which "Which one though?" would work but I don't know if the context in which you found it.