How do I add a 'CiviCRM ID' column to an activity report?
The possible way to add CiviCRM ID (Internal Contact ID) is to use the find activities -> From search , find activities, select search criteria ( some Activities status are default on 'Activity Status'), - hit search, use action menu to export activities, Select fields to export ->continue, on the next page you can select individual fields to export (including Internal contact ID) and the activity fields you wish to export.