If I arrive HK Airport after the last A12 bus departs at 00:10, what do I take to go to Shaukeiwan?

You can take Airport Express Train to reach HK Station and take a taxi to Central Station, where you need to transfer to subway Island Line to reach Shau Kei Wan. As I know, the last train of Island Line leaves at 00:56. So if you miss that, I suggest you take a taxi to reach your destination for convenience and security.