This is how you can debug console and as a pop-up.

var viewer = new Cesium.Viewer('cesiumContainer');
viewer.dataSources.add(Cesium.KmlDataSource.load('includes/Cesium/KMLData_for_abc_2015-08-04__2015-09-14.kml'))
.otherwise(function(e){
    console.log(e);
    alert(e);
});