The complete audit trail is not available through the TOPdesk API.
There's no API that provides a full audit log containing all field changes, including who changed a value, the old and new values, and the exact timestamp for every modification. The available history endpoints are limited to specific objects and use cases.
If you need to track specific changes, my recommended approach would be to configure logging actions through Action Management. With these actions, you can define exactly which events you want to capture and which information should be stored by using variables. This gives you more control over what is logged, for example the user who performed the action, the changed values, timestamps, or other relevant details.
This approach is often more suitable when you need a custom audit trail for specific information.