XmlReader.NamespaceURI Property

XmlReader reader = XmlReader.Create("book2.xml");

// Parse the file.  If they exist, display the prefix and 
// namespace URI of each node.
while (reader.Read()) {
  if (reader.IsStartElement()) {
    if (reader.Prefix==String.Empty)
      Console.WriteLine("<{0}>", reader.LocalName);
    else {
      Console.Write("<{0}:{1}>", reader.Prefix, reader.LocalName);
      Console.WriteLine(" The namespace URI is " + reader.NamespaceURI);
    }
  }
}       
reader.Close();

<book xmlns:bk='urn:samples'>
  <title>Pride And Prejudice</title>
  <bk:genre>novel</bk:genre>
</book>