Which subway line do you take from the World Trade Center to Chinatown?

It's very easy. You take the Downtown E train (of the A-C-E, the blue line) from 34th Street-Penn Station to the end of the line, the World Trade Center Station (at the corner of Church and Barclay Streets, northeast corner of the WTC site).

The WTC site is bordered by West Street to the west, Church Street to the east, Barclay Street to the north, and Liberty Street to the south.