When an incident is reopened using Reopen Incident Process Action Smart Task, the text user enters into Reopen Comments field does not get shown in or saved into the new incident.
The comment is left unsaved in the project.
This issue has been fixed in ServiceDesk 7.6 and newer.
Reopen flow is open to modifications in 7.5 (%ProgramFiles%\Symantec\Workflow\WorkflowProjects\SD.IncidentManagementSimple.Reopen.package).
A good way would be to open this project and edit the 'Add Comment to New Ticket' component to contain the comment. To add the comment to the existing Process Message - logical place to see the comment is in the Process Message body - you can add it to 'Add Comment to New Ticket' component, 'Configuration' Tab, the 'Information To Store' field - the variable with comment is called VarReopenComments. (Look at the attached screenshot for an example)