Immediately to the vets. You nor I would be able to tell if the skunk had a disease or worse yet rabies. Some diseases can be passed to humans so don't wait....immediately--ASAP>

 The skunk must have already been road kill in order for your cat to have eaten any part of a skunk. Even babies have the ability to spray and unless your cat has no sense of smell, it is highly unlikely it killed and ate a skunk. So, if it ate some road kill, the flesh wont hurt it but if it was diseased then the vet is where you should go to help your animal. The flesh may have been rotted from the heat and your cat has food poisoning or some feline equivalent.

 A trip to the vet is necessary. Call your local vets office and ask what to do. A cat, especially if he is overweight, can get VERY deathly ill if he goes too long without food, a condition of the liver called hepatic lipidosis, and can end up needing emergency care and a feeding tube. I wish your question was a bit more specific. I hope your cat is ok! This question is old now, so I hope all is well and that this answer can possibly help some one else.