You may legally ask if the handler has a disability (but not what the disability is.)
You may ask if the dog is trained to do a task to assist the handler in the disability.
You may ask what the task is.
You may not ask the handler to have the dog demonstrate the task.
You may require that the dog be housetrained and under the handler's control.
You may require that the handler never leave the dog unattended at the premises.
You may require that the handler provide all supplies and care for the dog.
Emotional support animals (ESA) are not service dogs. An ESA is not guaranteed access.
Therapy dogs, companion dogs, search dogs and other trained dogs are not guaranteed access.
PTSD dogs for disabled veterans are service dogs that do a task and are guaranteed access.
The suggestion to enter a number in a website is not accurate. True service dogs are not required to have a number, and any dog owner can get a number by paying that bogus organization a fee.
You may tell the guest that you are happy to accommodate a service dog but that you choose not to accommodate an ESA or other pet. Then say that you would like them to provide answers to the questions you are permitted to ask.
The whole ESA and fake service animal thing is reaching crisis proportions. It is really unfair to disabled individuals who need their service dog for sucessful basic daily living. I would encourage you to accommodate service dogs and exclude fakers. We allow dogs so that doesn't come up for us, but I just despise people that scam to bring a dog where pets are not allowed.