At a Salvation Army concert in Tiptree, Essex, UK a man sneezes into his Trombone.
To us, it sounds exactly as you might imagine, and also in the correct key. You can learn to play the Trombone in the book “Learn to Play Trombone! Book 1: A Carefully Graded Method That Develops Well-Rounded Musicianship“, though we’re not sure there is a section on sneezing.
Read an interview with Trevor Smith, the infamous sneezer, on the BBC Website.