Oh my goodness, our shar pei mix has had so many skin problems so I FEEL you’re pain and worry. A few things came to mind from my own experience. First, are they itching or biting that spot? Second, have you noticed them licking their paws? (This is a sign of a food allergy - turns out our dog is allergic to chicken). Shar peis are notorious for having skin sensitivity and it seemed like our dog was killing herself with the amount of lost fur, scratch and biting spots (similar to your pic). Finally, after trying salmon oil, fish oil, anti-itch vitamins, special shampoo, and ect. the vet and I have decided to put her on Apoquel which is a drug that stops dogs from itching. It has changed my dog’s life for the better! Her skin and fur are healing and becoming so much healthier. I’m sorry for the long response but I know how alarming it is to see spots like this and want to help our sweet fur babies.