What can I eat if I a broken mandible?

Ask your surgeon. There are many kinds of mandible fractures and there are different treatments for each kind. Some need surgery some just a soft diet. Ask your surgeon what is right for you.
Liquids and soft. A broken mandible requires prompt medical attention because of the risk of breathing problems or bleeding. If the jaw is wired already, you can only drink liquids or eat very soft foods.
Depends. Depends on whether or not your fracture has been repaired. And if so, are you wired or plated? If wired, just liquids. If plated or treated without plate or wire, non-chew diet. For detailed instructions, see oral surgeon.