Quarantine reports can be enabled for the shared quarantine or for individual quarantine user accounts.
From the shared quarantine or my quarantine views, users can enable their own quarantine reports by scrolling to the bottom of the listed emails and using the link shown here:
Only account contacts (those listed on the Account > account contacts page) are considered account administrators and have access to enable reports for the shared quarantine.
Account contacts can also set up quarantine reports for any quarantine user by going to the Settings > quarantine users page and editing an existing quarantine user by clicking on the row or creating a new one using the add button. The quarantine report settings are at the bottom of the form: