This stage is Bob-ombs Below (5-5). 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
When you the purple wall, toss a bomb into it or use your tail attack to break it. The first green star is found behind the wall.
Green Star 2
The second green star is found on a green glowing bunny on a circular platform.
Green Star 3
When you see the smiley cloud, jump into it to enter a secret area. Turn on all the floor switches to obtain the final green star.
After the second star you will see a cracked hole inside the wall. Toss a bomb into it to reveal a secret passage. Enter the passage and head to the right to collect the stage stamp.