Displaying data by views from external API I have made 2 db's one is of Drupal 8 and another is external, that is non-SQL(CouchDB) and to manage this DB I made an API with different endpoint(URLs) witch I can axes them by GET/POST methods. After correct request I get response 
 in JSON from my API.

When I create for example a user, content(node) or something else I save some info in my Drupal database and some info in my API db (I made alteration of the forms that create content by hook_form_BASE_FORM_ID_alter and this way I create content in my external DB).

My question is how to Display a data from a views, combining information form two Data-Bases?
If all you need to do is display data from the API, then you don't need to do anything special within views.  Just select that you'd like to view rendered entities of your users with a specific view mode. 



In the preprocess function for that view mode, you can hit the API and load the additional data that you need.  Data loaded within a preprocess function should cache, so it shouldn't hit the API on subsequent page loads.

function mymodule_preprocess_user(&amp;$variables) {
  /** @var $account \Drupal\user\UserInterface */
  $account = $variables['elements']['#user'];

  // custom code to hit the 3rd party API