The version of CKEditor is specified in various files bundled with its source.
ckeditor.asp:
Private Sub Class_Initialize()
version = "3.5.1"
...
ckeditor_php4.php:
class CKEditor
{
/**
* The version of %CKEditor.
* \private
*/
var $version = '3.5.1';
...
ckeditor_php5.php:
class CKEditor
{
/**
* The version of %CKEditor.
*/
const version = '3.5.1';
...
You can also find it by viewing a web page that has the editor, opening your browser console (e.g. Tools -> Web Developer -> Web Console in Firefox) and entering CKEDITOR.version
at its command prompt.