as @Kirill Polishchuk answered - SKUDetails is defined in http://tempuri.org/
he shows you how to get using XDocument
you can use alsow XmlDocument like this:
var dom = new XmlDocument();
dom.Load("data.xml");
var mgr = new XmlNamespaceManager(dom.NameTable);
mgr.AddNamespace("a", "http://tempuri.org/");
var res = dom.SelectNodes("//a:SKUDetails", mgr);