Robert Pattinson knows how to work a crowd. The “Twilight” hunk showed up an hour before the premiere of “Water for Elephants” to schmooze with fans Sunday night, sources said. His driver dropped him “at the top of the block” so he could stroll along West 54th Street and sign autographs. When a rep for co-star Reese Witherspoon saw Pattinson’s populist move, she quickly called her to get in on the act, a witness said. A car “screeched up 20 minutes before the film” and deposited her in the middle of the block. Witherspoon’s rep said, “Both actors came early to meet and greet their fans.”