Any new or unusual bump should definitely be evaluated by your veterinarian. It does not look like a blister. It could be anything from a cyst, a papilloma, a benign growth, an abscess, or something more serious. Your veterinarian may be able to do a needle aspirate and look at the cells under the microscope to give you an idea of what it is. If it is something serious, you want to get it taken care of while it is still small and while your Pug is still asymptomatic. I'm glad you're paying attention to your girl and checking her over--that will help you keep her healthier longer!