curl --request GET \
  --url https://api.hubapi.com/cos-domains/v1/domains/{domainId}

{
  "id": "1234567",
  "domain": "demo-hubapi.hs-sites.com",
  "primaryLandingPage": true,
  "primaryEmail": false,
  "primaryBlog": true,
  "primarySitePage": true,
  "primaryKnowledge": false,
  "manuallyMarkedAsResolving": false,
  "isResolving": true,
  "created": 1482867600000,
  "updated": 1482867600000,
  "isUsingHttps": true,
  "sslRequestId": "ssl-123456",
  "usedFor": "LANDING_PAGE"
}