Politifact.com Truth-O-Meter rulings from National: Donald Trump: "I watched in Jersey City, N.J., where thousands and thousands of people were cheering" as the World Trade Center collapsed.

We conducted an exhaustive search of newspaper and television transcripts on LexisNexis, looking for reports from September 2001 through December 2001 that made any mention of Muslims in New Jersey celebrating the 9/11 attacks.
http://www.politifact.com/truth-o-meter/statements/2015/nov/22/donald-trump/fact-checking-trumps-claim-thousands-new-jersey-ch/