As stated in the Documentation you may not be able to access it directly, instead you should call any Folder API function once CKFinder object has been loaded.
Note: the CKFinder.dataTypes namespace is not directly accessible (CKFinder.dataTypes is undefined). Data types are used internally by CKFinder and returned by many functions, like CKFinderAPI#getSelectedFolder.
The following example is an initialization in javascript of the CKFinder component which shows how to access the Folder datatype.
<script type="text/javascript">
var finder = new CKFinder();
finder.basePath = '/js/ckfinder/'; // The path for the installation of CKFinder (default = "/ckfinder/").
// Setting custom width and user language.
finder.width = '99%';
finder.defaultLanguage = 'es';
finder.language = 'es';
finder.removePlugins = 'basket';
//finder.selectActionFunction = showFileInfo;
//finder.resourceType = 'Images';
//finder.tabIndex = 1;
//finder.startupPath = "Images:/";
finder.callback = function( api )
{
api.openMsgDialog( "", "Almost ready to go!" );
api.hideTool( "f2" );//hide flash folder
api.openFolder('Images', '/');
var folder = api.getSelectedFolder();
//console.debug(folder);
folder.createNewFolder( 'New Folder' );
//api.setUiColor('white');
};
var api = (finder).create();
//console.debug(api);
//api.openMsgDialog("Sample title","Sample message."); //doesnt work here, CKFinder still not loaded.
</script>