This page of the Syberia: The World Before game guide contains a walkthrough of chapter Vaghen - Musician district, spring 1937. You'll learn how to complete the secondary objective related to the Ghetto and how to prepare the piano.
During this chapter, you'll have the chance to unlock the Leave a Trace and Parallel Investigation achievements. You can read more about it on a separate page of this guide: Trophies.
Investigate the Ghetto - secondary objective
You'll see the secondary objective when walking past the painting to the main square. Turn right into a narrow alley, go to the end of a cul-de-sac and look at the writing on the building on the left.
Talk to the man kneeling by the store with the broken window. Select any symbol and paint it on the drying cement.
Reach the main square
When the game starts, turn left and go straight until you reach the main square. Give Frau Beckmann a note when you talk to her.
Get the piano ready
Move the camera to the left and pull the lever down. Then look at the piano and put the Vaghen's hymn score on it. Finally, click on Begin.