Programatically adding new CKeditor instance
You're not supposed to use the CKEditor API directly. You could do that if you want to use CKEditor on something you control. But your DOM ID (edit-comment-body-0) indicates you're trying to do this for a "Formatted text" field in Drupal 8, which uses the filter system.
If you'd want to attach CKEditor manually, use the JS API provided by core/modules/editor/js/editor.js.

The integration between Drupal 8 and CKEditor is very solid/deep, in that Drupal 8 automatically configures CKEditor to match the text format's filter settings. And that integration is not tightly coupled to CKEditor: there's the Text Editor (editor) module that allows any text editor to integrate in a similarly deep way. But it means you should always use the APIs that editor provides.

For API docs, see:


https://www.drupal.org/developing/api/8/editor
https://www.drupal.org/developing/api/8/ckeditor
https://www.drupal.org/developing/api/8/filter


For the concrete relevant code, see TextFormat, editor_element_info_alter() and \Drupal\Editor\Element::preRenderTextFormat.