It's not a spot, but a small blister. It's a pimple, sometimes my dogs have it too. With a sterile needle and a disinfected skin surface, it can be carefully poked out and the contents squeezed out. Or if someone not skilled in medical treatments, they won't touch it. It disappears completely after a while (several weeks).
Must be checked, because it may not be pimple, but another type of skin lesion, which should not be pricked with a needle.
Fortunately, since it is outside in a visible place, the vet does not have to make embarrassing comments if you show him. ?