literally it's "you go to work with/as/by what?"
"by what [means]" -> how
I too am confused by the use of "gi" in this example. Can anyone explain it
Here's a case I would argue it would be better to accept the literal translation: "You go to work with what?" as acceptable. That would be still understandable to an English speaker (i.e., 'what method or means do you take to go to work?") and it would further your thinking of how to construct such a sentence in Vietnamese.
I think ' You go to work with what?' would be asking what do you take to work with you - briefcase sandwiches whatever.