Using JSM Internal Comments in monday.com
If you enabled JSM internal comments in monday.com you will be able to see any internal note made in a Jira Service Management ticket linked to a monday.com item. To differentiate the comments from the internal notes by the “Internal Note” indicator beside the comment timestamp.

Adding internal notes from monday.com
As a monday.com user, you can also add an internal comment for the JSM project, but keep in mind that normal comments and internal notes will be visible for everyone in monday.com.
To add an internal note from monday.com simply open the monday item with the linked Jira Service Management ticket, → go to the Jira for monday.com tab view → open the comments section → write your comment and check the “Internal Note” checkbox at the bottom of the editor.
