Generally speaking, a 3 year old Puggle should be approximately 15 to 20 pounds. If this is correct for your dog, then feeding about 3/4 cup to 1 cup a day is recommended. Split this amount in half to feed your dog twice a day. You might have to increase or decrease this amount based on your dog's weight and the type of food you are feeding. A good rule is that you don't want to see your dog's ribs, but you want to be able to feel them easily. http://www.dogbreedinfo.com/feeding.htm
An adult Puggle should have a diet that is quite similar to a Pug or Beagle. One or two cups of nutritious dry kibble daily is a good amount. However, the quantities can change depending on the dog's physical activity. Some are okay with one meal, but others prefer two. Always supply the Puggle with fresh, clean water.