The vet will do it. They draw the blood and sent it off. You can also get the kit your self online but you will have to take the kit to the vet to draw the blood. The website its:
Dog DNA Test | Mixed Breed Analysis | Canine Breed Testing and at the home page click buy now button at the top. The cost is 124.00 and the vet charged my 18.00 to draw the blood. I got mine online and took it to the vet because I did not know the vet also had the kits. Either way it cost the same. But its easier to let the vet do it. Hope this helps.