can anyone tell me which airport public bus goes to royal plaza hotel, hong kong?

By airport bus, transfer is needed on the way! I suggest you take bus no. E21 to get off at Sham Shui Po Station, Cheung Sha Wan Road. Then walk to Sham Shui Po MTR Station to take Tsuen Wan line to Mongkok station. Get out from exit D to walk to your hotel.

Or take Airport Express to Kowloon station and then transfer to free shuttle bus line K5 to your hotel directly.