In case anyone is interested:

I did the following:

        $("#fileTreeContainer").dblclick( function () { 

        	var treeView = $("#fileTreeContainer").data("kendoTreeView");	
        	var selectedNode = treeView.select(),
        	dataItem = treeView.dataItem(selectedNode);

        	if (dataItem.type == 'file'){
            	    // call your action to download a file or whatever
        	}     	 		
        });

dataItem.type is a property that i assign when building the JSON structure. This tells me if the selected item is a directory or a file. I need this because i use the doubleclick to download a file and obviously this is only for files, not for directories.