What I understood from your Question is, You are calling WCF service which is returning XML string having "result" node in it. And you want to read value of "result" node from XML string.
Try as below code.
string strXmlFromWCF="YourResultXMLFromWCF";
System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
doc.LoadXml(strXmlFromWCF);
System.Xml.XmlNode resultNode = doc.SelectSingleNode("result");
string result = resultNode.InnerText;
Alternate Solution -
string strXmlFromWCF="YourResultXMLFromWCF";
System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
doc.LoadXml(strXmlFromWCF);
string result = doc.DocumentElement.InnerText