using System;

using System.Xml;

using System.Xml.Linq;

using HtmlAgilityPack;

public class Program

{

    public static void Main()

    {

        var html = @"<div id='nome'>

    <p> <!-- this node --> 

    <strong></strong>

    </p>

    <br/><!-- this node --> 

    <span><!-- this node --> 

    <strong></strong>

    </span>

    <p><!-- this node --> 

    <span></span>

    </p>

</div>";

        var doc = new HtmlDocument();

        doc.LoadHtml(html);

        HtmlNode elementbyId = doc.GetElementbyId("nome");

        var nodes = elementbyId.SelectNodes("*");

        foreach (var htmlNode in nodes)

        {

            Console.WriteLine(htmlNode.OuterHtml);

            Console.WriteLine("-----------------------");

        }

    }

}