By federal government definition, a service animal can only be a dog (although guide horses are a thing) and the animal has to perform a physical function, not just provide emotional support. Some services are highly specialized and dogs train in puppyhood. Others, like supporting and redirecting a person with post-traumatic stress disorder, are things that a dog can be trained to do later in life. People can train their own dog if they have one, or adopt one from a shelter.
The dog’s breed or size isn’t important, which seems to lead to much of the confusion in these cases. PTSD dogs aren’t necessarily the familiar German Shepherd Dog or Golden or Labrador retrievers that work as guide dogs that most people are used to. They can be teeny terriers or muscular pit bulls, but they’re all able to behave themselves in public. In this case in Texas, the service dog is a Doberman, and is still in training.
His owner is a Marine veteran who served in the Gulf War, and says that the dog helps him to go out in public in spite of his post-traumatic stress disorder. (Many of the news stories about incidents like this feature combat veterans, but civilians can experience severe PTSD and benefit from service dogs, too.)
The Marine says that at the restaurant, a man emerged from a back office and kept asking whether he could see. He was then asked to leave because of his “attitude.”
If a person enters your establishment with a service dog, you can ask what task the dog performs for the person. You cannot ask what the person’s disability is, or why they require a service dog.