Eclipse has a feature called Bookmarks where one can make notes against specific lines of code and also a View to see all these bookmarks.
Does IntelliJ IDEA have anything like this natively or as an add-on?
On Mac you can add a bookmark with F3, then command F3 will bring up all of your bookmarks and you can add notes to them individually.
On Windows and Linux it's F11 and Shift+F11.
More info can be found in the official IntelliJ IDEA documentation: Bookmarks.