Can you give your dog aspirin?
No - aspirin (and all other human pain medications like Tylenol, Motrin, Advil, Aleve, ibuprofen, acetominophen, etc.) are toxic to dogs. They are very sensitive to the side effects and can develop a fatal stomach ulcer from the drug after even a single pill. Every year a number of veterinarians watch a dog die because the owner gave the dog aspirin to treat some sort of pain.
If you believe your dog would benefit from pain medication, you should make an appointment with your veterinarian. There are safe and relatively cheap medications that your veterinarian can prescribe for him.