WFAA-TV's Earl Jay Watson, known as Jay Watson may have been to the first person to mention the "Grassy Knoll."

At about 25 minutes into this video WFAA-TV's Jay Watson after talking to Bert Schipp who was at the Trade Mart and saw the motorcade speed pass on its way to Parkland Hospital tells what he saw, summarizes the news up to then.  "Ladies and Gentlemen let me bring you up to date, Jerry Haynes and I were within about 100 yards of where the president was shot this afternoon on the grassy knoll there...

This happens at about 27:14 in this video.