I found my dog with a hairless wheel and a granite in the middle and on the other side he has a similar granite that comes out with something white like fat or something and I'm very worried about that.
Hair loss can have different causes: infections, alopecia due to excessive licking or a insect bite or foreign body. Presence of some cyst, skin problems, etc.
The first thing you should do is take your dog to your vet in order to determine the diagnosis and the corresponding treatment.
All the best,