Ah....a German Shepherd. Looks like a nice dog and he sure has a beautiful black mask! Yes, he does look skinny but he is not going to put on weight if he is only eating that small quantity of food. So now you have to investigate all avenues which is what you are doing. Worms: there are a number of types of worms that dogs get. Some worming compounds do not kill all types of worms. Have the vet check a fecal sample to be sure that you are treating the correct worm. Secondly, dogs also get amoebic infections so have the vet check for that also. I think you better forget the milk. Adult dogs normally have trouble digesting milk. Now you need to increase the calorie count of what he is eating. If you are frying nonveg, pour the meat fat (find an amount he can tolerate without loose motion) on his other food, especially the dry Pedigree. Give him all the scraps from any non-veg like grizzle and fat. About bones: ONLY give bones he cannot chew up. Dogs should never be given chicken bones or small pork bones. They can sliver and perforate the intestines and kill the dog. ONLY give large bones. I would suggest getting a large bone hopefully with some meat on it, boil it and give to him to chew. He will enjoy and also hopefully all that chewing will increase his appetite. Also, are you exercising him? Go for long walks with him before dinner. Please keep posting on his status in case I can come up with any other ideas.
Hey, thanks a lot for the detailed reply! Will follow it and let you know. He is a very energetic pup, so I play with him every day, and make him tired, so that he sleeps peacefully. So I guess he gets his required exercise. Will check his stool sample with my vet to eliminate any worm infections.