What can my week old puppy, without mother, eat?

Eat? Nothing. The puppy needs puppy milk (NOT cow's milk).

Where's his mom?

We cannot find her. She's been gone since this afternoon.

You will need to go to your vet and purchase puppy formula and a bottle.

Ask your vet for advice on how much to feed for the puppies size. The amount will be small but feeding will need to occur every 2 hours, day and night.

You will need to manually stimulate the puppy to urinate and defecate as well. Mum usually does this by licking the puppy with her tongue. A suitable alternative is just a soft cloth dipped in luke warm water and rubbed over the puppies genitals.

The puppy will need to be kept in a warm room. Blankets don't do much as puppies under 2 weeks of age cannot regulate their own body temperature, the actual room needs to be kept warm.