Authorities are asking for the public’s help to identify a suspect they say robbed two highway gas stations at knifepoint in back-to-back incidents last Friday. First, the man pulled into a Shell gas station on Route 46 East in Parsippany-Troy Hills at about 7:54 p.m. and asked for gas, authorities said. When the attendant turned around, the man pulled a knife and demanded money, Morris County Prosecutor Robert J. Carroll, Chief of Detectives Christoph K. Kimker, and Parsippany-Troy Hills Acting Police Chief Richard Pantina said in a release Tuesday. About 10 minutes later, authorities say the…