var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
handler.setInputAction(function(click) {
    var pickedObject = viewer.scene.pick(click.position);
    if (Cesium.defined(pickedObject)) {
        console.log(pickedObject.id.position.getValue(viewer.clock.currentTime));
    }
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);