VET GURU: Unfortunately determining whether a mass is malignant or benign by appearance alone is near impossible. Fortunately, a lot of masses can be diagnosed using simple tests such as cytology (taking some cellular samples from an aspirate) or a biopsy (taking tissue samples from a little incision or tool). From the location you described, it may also be possible to remove the mass in its entirety via a local anesthestic without having to place Snoopy under general anesthesia. My suggestion is to have your vet look at the mass and do a few tests. Once you know the results, then you are in a better position to decide what the next steps will be--(ie remove w/ local or general anesthesia or do nothing and monitor for changes).
Hope that helps but in the mean time, wound care to the site since Snoopy is licking at it will not cause any harm. What may cause harm though, and invariably lead to much higher expense, is waiting too long. An ounce of prevention avoids a pound of cure.Good luck,