curl --request GET \
  --url https://api.hubapi.com/crm-object-schemas/v3/schemas \
  --header 'Authorization: Bearer <token>'

{
  "results": [
    {
      "id": "123456",
      "createdAt": "2020-02-20T18:07:11.390Z",
      "updatedAt": "2020-02-20T18:09:07.555Z",
      "properties": [
        {
          "updatedAt": "2020-02-20T18:07:11.802Z",
          "createdAt": "2020-02-20T18:07:11.802Z",
          "name": "my_object_property",
          "label": "My object property",
          "type": "string",
          "fieldType": "text",
          "groupName": "my_object_information",
          "displayOrder": -1,
          "calculated": false,
          "externalOptions": false,
          "archived": false,
          "hasUniqueValue": false
        }
      ],
      "associations": [
        {
          "id": "123",
          "fromObjectTypeId": "2-123456",
          "toObjectTypeId": "0-1",
          "name": "my_object_to_contact"
        }
      ],
      "labels": {
        "singular": "My object",
        "plural": "My objects"
      },
      "requiredProperties": [
        "my_object_property"
      ],
      "searchableProperties": [
        "my_object_property"
      ],
      "primaryDisplayProperty": "my_object_property",
      "metaType": "PORTAL_SPECIFIC",
      "fullyQualifiedName": "p7878787_my_object\"",
      "name": "my_object"
    }
  ]
}