Leave a comment anywhere on a note to ask a question, give feedback, or leave yourself a reminder. If the note is shared, anyone with access can reply in the thread.
Comments requires Notability Cloud.
Find the comment tool
The comment tool 
lives in your toolbox. Like any other tool, you can move it between pages or hide it.
You can also open a comment by selecting an existing comment pin with the Text tool or the Select tool.
Add a comment
Select the comment tool
in the toolbox.Select anywhere on the note to open a comment draft.
Type your comment.
Select the submit button, or press return, to post it. The thread opens so you can keep going, and a comment pin appears where you placed it.
To cancel a draft, press escape or select outside the draft.
Work with a comment
Move a pin: Drag the pin to a new spot. Pins stay inside the note boundaries.
Resolve a comment: Select the checkmark.
Delete a comment: While in a comment, select the
menu, choose Delete, then confirm.
On a shared note, anyone with access can reply. Each comment shows the name of the person who left it.
Use the comments panel
Open a note's options menu 
and select Comments, to see every comment in the note.
Select a comment to open the thread and jump the note to that spot.
Select the checkmark to resolve a comment.
Press and hold a comment, then select Delete, to delete it.
Show resolved comments
Resolved comments are hidden by default. Select the filter icon in the comments panel and turn on Show resolved to bring their pins back on the note.
This setting applies to one note at a time, so turning it on in one note won't change the others.