This diabetes disease can be screened out though symptoms like excessive thirst, frequent urination, excessive weight and hair loss. "Diabetes Insipidus" is a disease your dog is suffering from. To check the blood sugar of your dog, you can prick in leg or hip area to get its sample of blood. However, medically there is no specific place defined to take blood but for convenience of pets you can use leg or stomach for blood test. There are some instruments available to test sugar level. Try those.