As per Zendesk:
Triggers are business rules you define that run immediately after tickets are created or updated. For example, a trigger can be used to notify the customer when a ticket has been opened. Another can be created to then notify the customer when the ticket is solved.
Instead of managing Zendesk triggers via Zendesk itself, we instead use GitLab itself via the zendesk-triggers project. This allows us to have version-controlled triggers. For more information on managing Zendesk via the various GitLab projects, please review Using the sync repos.
As we have many triggers, and they change quite frequently, the best resource to see all the current triggers would be the zendesk-triggers project.