Hi @Jill150, since I cannot see what part of the form you are looking at, I will offer two suggestions. Either you are looking at info about yourself, therefore the ID number is your SSN or they are looking for Airbnb's tax ID number. That number is on the Earnings Summary that Airbnb sent you with your breakdown of number of reservations, nights booked, gross earning, airbnb service fees, total paid.
My CPA did my return for me (first time filing as an Airbnb host and new home owner) so I have not seen the forms since last year when my life was simpler.
It has nothing to do with individual guests, but your bookings as a whole. When you do your state and city taxes, you will have to put your business license number, if you are required to have one, in there somewhere as well.
Good luck. Jennifer