Hi Vojta,
Attach "click" event handler with FeatureLayer:
on(featureLayer, "click", function(evt){
var url = evt.graphic.attributes["urlFieldName"];
var windowFeatures = "menubar=yes,location=yes,resizable=yes,scrollbars=yes,status=yes";
if(url) window.open(url,'featureInfoWindow', windowFeatures );
});
Hopefully this help.
-Girish