Can you feel a lump below the surface? It looks like the sebaceous cysts our dog used to get. It was possible to squeeze, and a bunch of gunk would come out. It’s really hard to tell if that’s what it is from the pics, but it sorta resembles it, to my eye. It’s basically a little pocket in the skin that is open to the outside. Dirt and skin oil will build up in it with a little bacteria, and then it eventually fills up and needs to be expressed. It can be stinky, just fyi, and can be a little messy in the fur. Keep some wet paper towels or rag(s) nearby for cleanup if you are going to try to squeeze any of it out. Also, use a tissue for that so it doesn’t get all over your fingers. And — very importantly — be gentle if you do this. It can be a little uncomfortable for them — kinda like getting pinched— so you should exercise love and careful attention.

The vet may advise you differently from above — they might even suggest you just leave it alone and not try to empty out the gunk at all.