Answer
While custom reports are outside the realm of Altiris Support, here is some information about the database that provides a starting point.

To retrieve all comments related to an incident, query the Workitem table or the workitem_detail_view view. It may be helpful to show the version and modified time of the incident for each comment.

Workitem table syntax: 

select version, modified_on, comment from workitem where number = <insert desired number here>

workitem_detail_view syntax:

select workitem_version, workitem_modified_on, workitem_comment from workitem_detail_view where workitem_number = <insert desired number here>.

For more information about designing reports using Notification Server, see the documentation installed to \Program Files\Altiris\Notification Server\NSCap\Help.

In addition, Altiris Consulting Services can help with more complex reports.