It is illegal to ask this about a Service Dog. You may ask if the animal is used for a disability and what tasks is it trained for. Nothing else per the ADA can be asked. An Emotional Support Animal (ESA) you can ask for the doctor’s order and not allow if they can not prove it or just refuse to allow them unless it’s HUD/FHA housing, but proof is required for ESA’s to owners of rental per HUD/FHA.
Several airlines, I know Alaskian Airlines is one of them, as of this month are requiring proof that ESA’s are really ESA’s and 21 States will fine people who misrepresent a Service Animal or ESA now. These fake animals are actually hurting those with a real one, they want them stopped too. The vaction rentals on AirBnB are telling no pet allowed properties, they must accept them all Service Animals and ESA’s with no proof on ESA’s and it’s being abused for people to bring unrulely pets that damage the property and you can not charge a pet fee for them. Thus impacting those that really need them. No one wants them on planes, vacational rentals, and many other places because of the abuse of fake animals.