I wish there should be a bookmark option in learning curriculum alongwith ability to take short personal note in that bookmark, so that at the time of learning, if a learner feels something difficult he can bookmark & write short note about the problem and revise that later.
So my two suggestion are follows:
Adding bookmark facility in learning curriculum of freecodecamp courses.
Ability to put short notes in that particular bookmark.
You can suggest enhancements as GitHub Issues. Just as a personal note, the feature you’re suggesting would require a lot of work to implement and given the number of users that FCC has it could also put a large burden on the database. It’s possible that this feature could be adopted, but it wouldn’t be done soon, so I suggest using something like Evernote to do what you want for now.
Typically a programmer would put any notes about their solution in the code itself as comments. You could save your solutions (either locally or using something like GitHub) and use comments for notes to yourself.