curl --request GET \
  --url https://api.hubapi.com/integrations/v1/{application-id}/timeline/event-types/{event-type-id}/properties

[
  {
    "options": null,
    "propertyType": "Numeric",
    "name": "NumericProperty",
    "id": 1,
    "label": "Numeric Property",
    "eventTypeId": 260
  },
  {
    "options": null,
    "propertyType": "String",
    "name": "StringProperty",
    "id": 2,
    "label": "String Property",
    "eventTypeId": 260
  },
  {
    "options": [],
    "propertyType": "Enumeration",
    "name": "NoOptionsProperty",
    "id": 3,
    "label": "No Options Property",
    "eventTypeId": 260
  },
  {
    "options": [
      {
        "propertyId": 4,
        "label": "Some Label",
        "value": "OptionValue"
      }
    ],
    "propertyType": "Enumeration",
    "name": "EnumerationProperty",
    "id": 4,
    "label": "Enumeration Property",
    "eventTypeId": 260
  }
]