This should give you an idea on how to do it:
using System.Linq;
using System.ServiceModel.Syndication;
using System.Xml;
using System.Xml.Linq;
SyndicationFeed feed = reader.Read();
foreach (var item in feed.Items)
{
foreach (SyndicationElementExtension extension in item.ElementExtensions)
{
XElement ele = extension.GetObject<XElement>();
Console.WriteLine(ele.Value);
}
}