You can find an e-notes summary of Music for Dolphins at the following link: https://www.enotes.com/topics/the-music-of-dolphins. In addition, you can find lesson plans, including an author interview with Karen Hesse, an audiobook excerpt from the novel, and lesson plans related to the novel at the following link:https://www.teachingbooks.net/tb.cgi?a=1&tid=4769.
To access the lesson plan directly, you can go to the following link: https://multcolib.org/music-dolphins. At this link, created by the Oregon State Library, you can find questions related to the novel. These questions involve more concrete questions such as "What makes Mila want to return to the sea?" and deeper, more inferential questions such as, "What do you think the title means?" This link also includes activities, such as listening to Mozart (as Mila does in the novel) and writing down one's thoughts and feelings as one listens to the music. Finally, there is a suggested snack--goldfish crackers--to accompany the novel.
Below are links to one site with questions (no answers) and an activity and another site with a short lesson plan. I also including a link to lesson plans to other Hesse works.