Kind of like a riddle for me to decipher.
I think the technically correct way to write it would be: Tom asked, “Which is correct, 6'1" or 6'1,"?"
The problem is that the question can’t be properly reflected in a verbal statement (dialogue if you will) because the comma is unspoken. If Tom’s question was read out loud, it would sound like this, “Which is correct, six foot one inch or six foot one inch.”
I need to check, but I think the proper way to represent numbers in dialogue is to spell them out rather than using The Arabic numerals.