Its a federal law that you cannot ask for documentation. You can only ask two questions. 1. Is the dog required because of a disability 2.What work or task has the dog been trained to perform.
I have a very good friend who has a service dog for health reasons. He takes the dog everywhere.
Service dogs are allowed anywhere, then there are ESA’s, emotional support animals, they can not be excluded from rental homes but are not allowed to be taken into businesses and restaurants because they have not received training, I don’t think that excludes them from cabs, buses or planes.