All you have to do is create a new JavaScript (The placement: All pages).

Code:

/*
 *  Application: CKEditor
 *  Date: 30/04/2018
 *  Version: 1.030042018
 *  Copyright (c) CKSource and Adapted to forumotion by Daemon <help.forumotion.com>
 *  This work is free. You can redistribute it and/or modify it
 */
$(function() {
    if (!$.sceditor) return;
    $.ajax({
        type: 'GET',
        url: 'https://cdn.ckeditor.com/4.9.2/standard/ckeditor.js',
        dataType: 'script',
        success: function() {
            CKEDITOR.replace('text_editor_textarea');
        },
        error: function (jqXHR, textStatus, errorThrown) {
            if(jqXHR.status == 500) {
                console.log('Internal error: ' + jqXHR.responseText);
            } else {
                console.log('Unexpected error.');
            }
        }
    });
    $(function() {
        $('#text_editor_textarea').sceditor('instance').destroy();
    });
});

[Tutorials] CKEditor Apmbzuz

For more advanced users, I leave the editor configuration guide link: https://docs.ckeditor.com/ckeditor4/latest/api/index.html

If you want to add an extra tab to host images on Servimg, read the following message: https://help.forumotion.com/t155678-tutorial-ckeditor#1071520

Enjoy!