What does a 9-week old puppy eat? Hard dog food? Soft dog food? Any milk? Anything special? Is it allowed to have grains, a little piece of lean meat? Any advise?

Did you not get a diet sheet from the breeder? If you did then stick to what is recommended on it as good breeders know what best suits their dogs. If the breeder forgot to give you the sheet then contact him/her and ask for one.

Puppies of that age need 3 or 4 meals a day. If you are feeding a dry food moisten it with water or salt-free stock before giving it to the pup, and always make sure that plenty of fresh water is available. My pups were fed on mushed up cooked meat and vegetables, raw chicken necks, a little very good quality dry puppy food, raw mince, occasionally supplemented with sardines, egg yolk, or cottage cheese. You can add a little cooked pasta or rice, but not all dogs will tolerate grains, especially wheat products. I have never given milk, but if you do so then I believe goats milk is preferable to cows milk.

Really your breeder is the best person to advise you.