T809 is going from Guangzhou to Hong Kong (kowloon) . Then How to go to Hong Kong Airport ?

You can take the subway. You need to take the West Rail Line from Hung Hom to Nam Cheong first and then change to Tung Chung Line and get off at Tsing Yi Station. Finally change to Airport Express and get off at Airport Station. The trip will take around 90min.

The way above takes around 65min as I know. Apart from that, there is a better choice without any transfer. Bus no. A21 can directly take you from Hung Hom Railway Station, where this train will arrive, to HKIA. The bus fare is 33HKD and the duration is around 70min