The following code line is working fine...

XmlNode sslNode = appHostNode.SelectSingleNode("sites/site[@name = 'www.wow.com']/ftpServer/security/ssl");

Now I want to pass a variable instead of 'www.wow.com'... please guide
how can I do it....

Have you tried:

string variableName;

And using this in-line:

'" + variableName + "'