A teen-ager sought for shooting a motorist during a traffic dispute in Studio City six weeks ago pleaded innocent to attempted murder, a day after his capture on a Hollywood street. Thomas Robison, an 18-year-old transient, was being held in the Los Angeles County jail in lieu of $500,000 bail. Police had been looking for Robison for the Aug. 1 shooting at the intersection of Ventura and Laurel Canyon boulevards in which stunt man Henry Kingi, 43, estranged husband of actress Lindsay Wagner, was wounded in the arm and chest after he got out of his car and exchanged words with occupants of another vehicle. Police said Robison pointed a gun at Kingi's head and pulled the trigger, but it failed to fire. He then allegedly kicked Kingi in the groin and pulled the trigger again, with the gun firing this time.