This hidden star can be found in the Cataquack to the Skies level in Gold Leaf Galaxy. Gold Leaf Galaxy is located in the Engine dome.
First off, head up the path from the starting location and use the cataquack in the pen to propell yourself over to the area with the large redwood tree. At the back of the tree you’ll find a bubble blower. Jump into one of its bubbles and you can then use your star cursor to blow the bubble in whichever direction you need it to go. Use the Bubble to ring the bell that’s slightly above the bubble blower.
Once you’ve rung the bell, a trail of musical notes will spawn going up and around the tree. They are on a timer, but you have plenty of time to grab each of the musical notes so don’t worry if your bubble strays from the path for a second. Once you’ve collected all notes, you’ll be rewarded with a Power Star!