tern.jsduck provides the ckeditor tern plugin which gives you a support for CKEditor.

After installing and converting your project as Tern Project, go at Tern project property, click on Tern / Modules item and select the ckeditor tern plugin and the version :

After that you can benefit with CKEditor completion :

Completion works for CKEditor method :

Web Browser

You can play with online demo which uses CodeMirror (inside Web Browser).