Nothing except the ticket itself is shown, no ticket lists, FAQ or anything else. It is also possible to define which parts of the ticket that should be visible, consequently only showing specific fields.
The ticket can also be anonymous, so the external ticket operator will only be able to see the subject of the ticket and not who sent it.
The pop-up which is shown when a ticket is closed, is not editable for external ticket operators. This means that if, for example, the default setting is that an e-mail should be sent to the customer, this cannot be changed by the user. You can also make the default setting not to send e-mail to the customer, but back to the support team, and they will email the customer.