Can we catch shanghai subway line 2 from pudong airport after 24:00 to downtown?

I'm afraid not. The MTR line 2 closes operation around 22:00 depearting from the airport. I suggest you take the Night Shuttle Bus Line, which operates from 23:00 (T1), 23:05 (T2) till 45 minutes after the last flight. It can take you to the downtown after midnight.