Here you go...
XmlDocument xDoc = new XmlDocument();
xDoc.Load("Query.xml");
XmlNamespaceManager xnm = new XmlNamespaceManager(xDoc.NameTable);
xnm.AddNamespace("schemaLocation", "loc");
xnm.AddNamespace("payload", "loc2");
xnm.AddNamespace("a", "http://www.w3.org/2001/XMLSchema-instance");
xnm.AddNamespace("x", xDoc.DocumentElement.NamespaceURI);
Inner Text For Query:
xDoc.SelectNodes("//x:Query", xnm)[0].InnerText
Inner Text For QueryId:
xDoc.SelectNodes("//x:QueryId", xnm)[0].InnerText
a:schemaLocation Attribute:
string namespaceURI = xnm.GetNamespacesInScope(XmlNamespaceScope.Local).FirstOrDefault(el => string.Equals(el.Key, "a")).Value;
var x = xDoc.DocumentElement.Attributes["schemaLocation", namespaceURI].Value;