This stage is Shifty Boo Mansion (3-3). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars.
Game Play Walkthrough Video
Green Star 1
Jump into the first Boo painting to be transported into the room with the first green star.
Green Star 2
At the room with the moving bookshelves. Move your way to the left side of all the bookcases to reveal the second green star.
Green Star 3
Get on top of the couch next to a door. The green star is disguised as a green pipe, get near it to claim your last green star.
Hop onto the first couch that you see in the stage. The couch will rise and lead you to the stamp for the stage.