GetAttribute：

XmlDocument doc = new XmlDocument();
    doc.LoadXml("<book genre='novel' ISBN='1-861001-57-5'>" +
                "<title>Pride And Prejudice</title>" +
                "</book>");

    XmlElement root = doc.DocumentElement;

    // Check to see if the element has a genre attribute.
    if (root.HasAttribute("genre")){
      String genre = root.GetAttribute("genre");
      Console.WriteLine(genre);
 

   

SelectNodes:

XmlDocument doc = new XmlDocument();
    doc.Load("booksort.xml");

    XmlNodeList nodeList;
    XmlNode root = doc.DocumentElement;

    nodeList=root.SelectNodes("descendant::book[author/last-name='Austen']");

    //Change the price on the books.
    foreach (XmlNode book in nodeList)
    {
      book.LastChild.InnerText="15.95";
    }

    Console.WriteLine("Display the modified XML document....");
    doc.Save(Console.Out);


GetElementsByTagName:

    XmlDocument doc = new XmlDocument();
     doc.Load("2books.xml");

     // Get and display all the book titles.
     XmlElement root = doc.DocumentElement;
     XmlNodeList elemList = root.GetElementsByTagName("title");
     for (int i=0; i < elemList.Count; i++)
     {  
        Console.WriteLine(elemList[i].InnerXml);
     }