Featured Image

The featured image is linked to in the https://api.w.org/featuredmedia link:

"_links": {

  // [...]

  "https://api.w.org/featuredmedia": [
    {
      "embeddable": true,
      "href": "http://demo.wp-api.org/wp-json/wp/v2/media/15"
    }
  ],
  "https://api.w.org/attachment": [
    {
      "href": "http://demo.wp-api.org/wp-json/wp/v2/media?parent=16"
    }
  ],

  // [...]
}

Please review the documentation before opening new support threads.