“What do I owe you?”
You're going to go to a concert with your friend. Your friend bought the tickets, and now he's giving them to you. You want to know how much they cost, so that you can pay him back. This is what you ask him.
What do I owe you?
If you "owe (someone)" money, it means that you are supposed to pay that person:
He owes me twenty dollars.
Reasons that you might owe someone money include:
- you borrowed it from them
- you broke something that belonged to them
- you lost a bet
- you're buying something from them
You can also "owe" other things, like favors:
I owe him a favor because he helped me move a couple of months ago.
"Owing a favor" means that someone did something nice for you, so you need to do something nice to repay them.
This is a question that means "How much money do I owe you?"
A: Here you go.
B: Thanks. What do I owe you?
You ask "What do I owe you?" in casual situations. A slightly more formal version is:
How much do I owe you?