Looks like a few abnormal scales, femoral pores and dirty underbelly.
I suggest soaking him for about 20 minutes in luke warm water (around 80F) and with an old soft toothbrush and very mild soap (like ivory..definitely unscented) (basically just run the brush over a bar of soap once or twice) and gently scrub the dirty areas. After he's been soaking for 20 minutes any dirt or dried skin should come off easily with gentle circular motions with the toothbrush.
Scale rot is almost always caused by a wet dirty environment more than the typical dry environment in a dragon's cage. Fungus can also cause similar marks but I don't think that is what is here in your case.
Definitely try the bath and gentle scrubbing, rinse and look again. It isn't unusual for dragons to get dirty if they run through their poop before you can spot clean.
It will also be a good time to clean up the cage too, if it hasn't been done recently.
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PHLdyPayne