curl --request GET \
  --url https://api.hubapi.com/integrators/timeline/v3/events/{eventTemplateId}/{eventId}/detail \
  --header 'Authorization: Bearer <token>'

{
  "details": "<p>Registration occurred at Jan 30, 2020, 1:13:25 PM</p><h4>Questions</h4><p><strong>Who&#x27;s a good kitty?</strong>: Purr...</p><p><strong>Will you stop playing with that?</strong>: Meow!</p><p>EDIT</p>"
}