Possible Clues:

• Christmas coming up, put notes in as composer of 'Happy Xmas'
• John — (Beatle)
• 'The U.S. vs. John ___' (2006 documentary)
• See 53-Down
• John of rock
• Letters dropped from six answers 'come together' here
• John --, songwriter, vocalist and rhythm guitarist
• 'Give Peace a Chance' singer
• Thomas of "Reno 911!"
• Song writer, initially lazy, takes an age to pen notes