My dog got bit by another dog. What should I do for the infection?

Oh dear, poor Jack! Dog bite wounds can become infected quickly and can cause far more damage under the skin than is visible on the surface. I strongly recommend taking Jack to his vet for evaluation since surgery can be necessary for many bite wounds to assure that the wound is clean, tissue is healthy, and that underlying organs and structures have not been damaged. The vet will also likely prescribe antibiotics (cephalexin, cefpodoxime, amoxicillin-clavulinic acid are typically used in these cases) and a non-steroidal anti-inflammatory medication (such as carprofen, deracoxib, or meloxicam) if his liver and kidney blood values are normal. The vet will also likely recommend an e-collar (cone) to prevent Jack from licking or scratching at the wound, unless the collar would directly rub on the wound and cause further irritation. I hope this helps and that Jack feels better soon!