Teju Cole , who won the 2012 PEN/Hemingway Award for his book “Open City,’’ got a helping hand after being called up to the podium to accept the honor during the Hemingway Foundation/PEN Awards ceremony at the John F. Kennedy Library on Sunday afternoon. Other writers called up to the stage to be greeted by Ernest Hemingway ’s son Patrick during the celebration included PEN/Hemingway finalists Amy Waldman , author of “The Submission,’’ and Stephanie Powell Watts. . .