using System;

using System.Linq;

using System.Xml;

using System.Xml.Linq;

public class Program

{

    public static void Main()

    {

        string xml = @"<?xml version=""1.0"" encoding=""utf-8""?>

<data>

   <text>How to get <bold>all</bold> this string's content?</text>

</data>";

​

        XDocument doc = XDocument.Parse(xml);

        var textClasses = from n in doc.Descendants("text").DescendantNodes()

                          where n.NodeType == XmlNodeType.Text

                          select new { text = ((XText)n).Value, bold = n.Parent?.Name == "bold" };

        foreach (var tc in textClasses)

        {

            Console.WriteLine("text: " + tc.text + ", " + "bold: " + tc.bold);

        }

    }

}