Getting the TrackingId on a page.

array.js

ga(function() {
  var trackers = ga.getAll(), ret = [];
  for (var i=0; i<trackers.length; ++i) {
    var tracker = trackers[i];
    ret.push(tracker.get('trackingId'));
  }
  console.log(ret);
});

single.js

ga(function(tracker){
  console.log( tracker.get('trackingId'));
});