Dogs can get ringworm, but what people usually think is ringworm is more often something else (this is straight from the derm department, but I will check in with them today if you would like). It's far more common in cats and cats may not even show any lesions. I do believe there is a microsporum and a trichopyton species that dogs can get.
While not as common, dogs can definitely get ringworm. A friend brought home a symptomless cat from the shelter and both her dogs and other cat came down with it.
You can always treat as ringworm or a lesion or injury and if it doesn't improve, check with your vet.