gistfile1.js

// if you're using DataSource.IO see  http://yuilibrary.com/yui/docs/api/classes/DataSource.IO.html#event_response
// if you're using DataSource.Get see http://yuilibrary.com/yui/docs/api/classes/DataSource.Get.html#event_response

// listen for the DS response as ....

myYUI3DataSource.after('response', function(o) {

/* the response object contains the following;
   o.response.meta,    =  meta fields parsed from the DataSchema "metaFields"
   o.response.results, =  results parsed from dataSchema and "resultsListLocator"
   o.response.error    =  any error
*/

// BEST approach, set a breakpoint in Firebug on first line in this listener and inspect o ...

});