Click the icon at the bottom left of the comment to cycle it between the following states:
By default, comments are assigned a None status. By clicking To-Do you turn it into a to-do comment. When the task is complete, you can cross it off by marking it as Done.
Note: All team members can see the to-do status of a comment, so marking it as to-do will show that icon for everyone on the team.
To make it easier to see your task list, you can choose to only show to-do comments. To do this, click Filter Comments underneath the comment text field and then select To-Do Only. You can choose to hide comments marked Done.
To-do comments can only be viewed on the player page of the site but the Kollaborate Adobe Panel plugin has a dedicated section for viewing and crossing off to-dos.