Hi Guest
ServiceDesk Plus keeps an audit trail of all interactions on a request.
This audit trail is kept in a table called workorderhistory
You have two "trigger" events so its just a matter of finding out how they are stored in the workorderhitsory table and then reporting on those
More info and details of the logic can be found here: http://set3manageengineuk.blogspot.com.au/2013/12/custom-reports-for-servicedesk-plus_4.html