I am a Pakistani citizen. I have a Schengen visa. Can I travel to New York from London or do I require any other document or visa to travel?
You require a US visitor visa (tourist visa) if you want to travel to New York from London, because a Schengen visa will not get you into the US.
As a Pakistani citizen, you will require a US visitor visa to enter the United States. A Schengen visa is not sufficient.