The Respectful Pianist is a Seasonal Spirit in Sky: Children of the Light that was first introduced in the Season of Rhythm. Don't worry if you missed the season, because you can still find the Pianist and get the sweet emote.
Respect Emote — Winter Piano | Duck Mask | Triangle Hair Sky: CotL Travelling Spirits (rhythm)
Here you will find the Respectful Pianist in Sky: Children of the Light.
Make sure to complete the game and watch the credits before attempting to find a Seasonal Spirit, including the Respectful Pianist. Seasonal Spirits will only appear to players who have played the game at least once.
You can find the Respectful Pianist in Sky: Children of the Light in the Graveyard section of the Golden Wasteland (the Fifth Realm).
