Any breeder  of  purebred dogs is up to the breeder to know where it should be docked on a puppy.  If you are unable to do it yourself, and not all breeders can do it -too squeamish, then you should be able to direct your Veterinarian, who is a doctor as he said, where to dock it.  
If you don't have a Yorkie breeder mentor to help you, read your breed standard about the tail, it is there.        |