hi, which bus do i take from shenzhen train station to central hong kong?

By bus, tranfer is needed. Take a taxi to Huanggang Border to take a cross-border coach to Tsim Sha Tsui. Then take Tsuen Wan line to Central.

I would recommend you travel by rail: From the train station, walk south around 380 yards to Luohu Port. After pass the custom and enter HK, you can take East Rail Line to Kowloon Tong Station. Then transfer to Kwun Tong Line to Mong Kok Station and take Tsuen Wan Line to Central Station, Exit F. It spends around 70 mins. And the ticket fare is 46.3 HKD per person.