By default, teachers can only view the lesson notes from their own lessons. However, in the scenario that a teacher is substituting and needs to view notes from lessons the student has had with a different teacher, they can follow the steps below:
Click on the lesson on the calendar and click on "View" in the pop-up.
Click on the student's name to view their profile.
Scroll down to the "Recent Lessons" section to view the student's 10 most recent lessons.
Click on a lesson title in this section and they can view the lesson details including any notes from these lessons.
If you would like to limit the "Recent Lessons" and "Upcoming Lessons" sections displayed on a student profile in teacher accounts to only lessons taught by the teacher viewing the profile, you can follow the steps in this article: Limit Teacher View of Student Recent & Upcoming Lessons to Only Their Own.