There are 2 reasons why you may not be able to see to-dos using the Adobe CC add-on.
The proof hasn’t been returned with a to-do list yet.
The proof must have to-dos marked and have been returned to the proof owner with a to-do list. In the web-app we display proofs that have been returned with a to-do list with a green overlay and they will be sitting in your inbox (if you are the proof owner or editor).
In InDesign only, if you are viewing the artwork in Preview mode, the pins will not be visible since they are non-printing items. Preview mode will only show printable items.
To turn off preview mode, in InDesign go to View -> Screen Mode and select Normal