As far as I know, Zammad doesn’t have any add-ons yet. Therefore, there is no way to integrate a customer satisfaction survey into Zammad directly without coding it yourself.
However, a possibility would be to use a 3rd party software, such as LimeSurvey. You can send a URL to the survey in the email that the user receives upon the closure of the ticket and include dynamic URL parameters such as the ticket ID or the agent that is currently assigned to the request.
You can insert images as rating objects (like thumbs up/down, smileys or smth similar) or text (Good - Neutral - Bad) that would link to your survey.
A disadvantage of using a 3rd party survey software is security. Because the information from the ticket (agent, ticket ID etc.) have to be transmitted to the survey software over URL parameters, users could easily manipulate these parameters and submit feedback for tickets they don’t even own. A security measure here would be to include the customer name in the URL parameters and later verify (manually or over a script that connects to the Zammad database) that the provided customer name matches the owner of the ticket. This works with other attributes as well (such as the ZIP code of the customer).
So for a full agent performance report of an agent you would have to merge the survey results and the Zammad reports (escalations etc).