I'm sorry that you're dealing with this, and I'm not trying to scare you, but that very much looks like a Yellow Fungus infection to me. I don't know how much you know about Yellow Fungus, but it's a very difficult fungal infection to treat because it grows both internally and externally at the same time, and as a result of this it requires that the Dragon takes both a oral Anti-Fungal medication and then also has a daily, topical Anti-fungal treatment at the same time. It is extremely hard to get rid of, and it often requires many months of treatment with both the oral medication and the topical medication. The sooner you start treatment, the better chance you have of treating it successfully.
You very much need to find either a Certified Reptile Vet or at the very least an experienced Reptile Vet with Dragon experience, and you need to request that they ONLY do a simple Skin-Scraping test of the area, and then send it out to a lab for testing. This is very non-invasive and cheap procedure, and it's very important that you get it done ASAP so that if it is Yellow Fungus you can get your Dragon on the oral Anti-Fungal medication, Voricozanole is the one that people seem to have had the most success with, and then also the proper topical Anti-Fungal treatment.