How can I GET Custom External Data in tasks?

Set IDs to tasks, I can get a task by external-ID with the request{{external-ID}}.

But I cannot find how to get the external IDs in other way.
For example, in the webhook, an Event has a ID for a task but no external-ID.
I can get a task by its ID with the request{{ID}}, but there’s no external-ID in its response.

How can I get external IDs of the tasks??

It’s my misunderstanding.
There’s an external ID in the response.