How can i decorate homemade dog biscuits?
You can use animal (hide) glue to make the sprinkles stick, similar to the adhesive on some envelopes that can be licked (or moistened otherwise) to activate the 'stickyness'. The content of the glue is not really that far off from the ingredients in dog food.

Any gelatinous based adhesive would also probably do. While they offer no nutritional value, they are edible.

Non toxic paste, such as used by young school children would also work, but I don't know if the color would ruin the presentation you're trying to achieve. I'd go with the animal glue if you're able to source it. Just melt it down and use a fine paint brush to paint the dog's name, apply the sprinkles and let dry, then shake / blow off the excess.