u/Lower-Put8118

It’s not any of the main musical numbers, it plays multiple times from the gramophone (I think it is, she winds it up) Sally owns. She plays it when she first tries to seduce Brian. There’s other instrumentals I’ve tried to find from this movie of the actual numbers that feature in the movie (specifically the theremin cover of ‘Willkommen’), but I don’t think they exist as separate recordings.

It’s in the background of this scene: https://youtu.be/xxtRr32p6pc?si=ixmHZwgsgntE6xLK