I know this is going to sound harsh, but it is what is best for the fish and not the keeper. It is up to you to decide what to do from here.
1) The ammonia should read 0. There may be a mini cycle or something happening in the tank that is not keeping the water at its best. Pristine clean water is the first line of defense in the healing process. That just isn't going to happen in that tank. The reason being:
2) The tank is too small. The bioload of those fish (especially the dog face) will require MUCH more filtration and space than you are currently providing. The dog face should be in a 100 gal tank all by itself, the porc will need about 120 gallons.
3) Diet. Shrimp are good as a treat but lack the nutritional value required to keep up their immune system. They need shelled crustaceans such as clams, mussels etc.. Never feed cooked foods to them. If you want to read more on feeding shrimp please read this article: Thiaminase
My first guess is that it is a lion fish sting. The spacing of the injury seems to indicate that. It looks like 3 small puncture marks, 2 of which have become badly infected. That is just a guess.
What is different is the fact that the area around the wounds hasn't turned grey or black yet, that would be proof of a lion fish sting.
Lion Fish and puffers are a TERRIBLE combination. Puffers usually can't resist nipping at those long beautiful fins and usually end up getting killed because of it.
Which leads my to the next theory: The Dog Face puffer may have taken a a swipe at the Porc. Puffer bites are almost perfectly circular but usually they don't break the skin. DF puffers do have some nasty teeth that Porcs don't have.
In either case, the fish should be held in a hospital tank with super clean water, an excellent diet with supplements. Have you posted on Marine Depot? Kelly will be able to advise a treatment method and possibly a better diagnosis.
If it is a lion fish sting... I have no idea of the treatment. I have never seen a puffer survive one.