There are a few reasons why your dog's jaw might quiver. It could be a sign of pain, or it could be a neurological condition. If your dog is in pain, the quivering might be due to an injury or infection. If the quivering is accompanied by other symptoms, such as vomiting or lethargy, it's important to take your dog to the vet for an examination.
Neurological conditions can also cause jaw quivering. One example is myoclonus, which is involuntary muscle twitching. Myoclonus can be caused by infections, tumors, head trauma, and more. If your dog has myoclonus, he'll likely have other symptoms as well, such as seizures or muscle spasms. Again, it's important to take your dog to the vet for an evaluation if you notice any unusual Symptoms