For the Boogie Down challenges, you'll need to visit and play the sheet music of an oversized piano. To do this, all you have to do is go south of Lonely Lodge, between the city tower and the abandoned heroes' mansion.
For the Prestige version of the challenge, you will have to play on the piano the notes specified on the score on the desk placed opposite. There will only be 5 notes to play, which must be carefully observed. The code being C, E, G, E, C, do it in order to complete the challenge, being careful not to hit any other note, and the piano will complete the composition for you. To better help you understand, we offer an explanatory video.
As a reminder, it's easier to complete this challenge in Team Rumble, since with the respawn, you won't have to worry about dying.