The default "Save" button is not available if you're not using the "replace textarea" method since CKEditor 4 and even in that case it's enabled only in wysiwyg mode.
This is just that plugin but removing those restrictions so you're allowed to use it and to hook into the command to do whatever you need.
Usage: In this builder remove the "Save" plugin and add this one. You're done. Now the button is always available and you can hook on the "save" event of the editor to save your data.