From chungking mansion nathan where is bus stop A22 going to the airport?

Bus A22 does not stop on Nathan Road and it just stop near Jordan Station. If you want to take, you can go to Woosung Street, Jordan Road or Kowloon Union Church, Jordan Road to take.
From your hotel, you can walk along Nathan Road to reach Jordan Station and ask the local people to find the two station I told you.
Actually, if you want to go to airport from Chungking Mansion, you can take A21 at Haiphong Road, Nathan Road.