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It really depends on what you are currently studying in the class. There is so much to novel structure that if you noted everything there is to note you could write a whole new book. Some examples of other things you could note: setting, story structure, conflict and resolution, use of literary devices such as irony and allegory. Do I need to go on because I could probably list another dozen just off the top of my head. What you really want to do when reading for class is consider what class the reading is for and note the things in the novel that relate to the class. For example, your notes for a Lit class are going to be different that those for a creative writing class even if you are reading the same novel. Also consider what is currently being discussed in the class. In other words, if the lecture for the week was on the effective use of metaphor, you will want to look for examples of metaphor in your reading. Bottom line is be cognizant of what you are currently studying and your notes should reveal themselves. I'm not sure if this sufficiently answers your question, but the list of "notes" to take from a novel is so broad, this is the best I can give you.
i note imporant events , major events ... bc later youll have to probably sum up your book or tell about it ... if you note main events you can kinda put some big exciting things about the book to tell someone ...... also main characters so that you keep tract of everyone & who they are in the book .
i always noted big words i didnt understand . so later i could google them & understand better and learn new words