If you have the values of the content type as mention. Below is just an example to guide you. there are other way to do the same.
Use the web service for the list
//get the name of the file
XPathNavigator xnDoc = this.MainDataSource.CreateNavigator();
//Create a Navigator object for the field that you want to set.
XPathNavigator TitleDescription = xnDoc.SelectSingleNode(”/my:TitleDescription”, this.NamespaceManager);
//so now I assume you will have the name of the file or what you are queryn for.
SPSListWeb.Lists listService = new SPSListWeb.Lists();
/*Authenticate the current user by passing their default
credentials to the Web service from the system credential cache.*/
listService.Credentials = System.Net.CredentialCache.DefaultCredentials;
listService.PreAuthenticate = true;
/*Set the Url property of the service for the path to a subsite.*/
listService.Url = “http://xxxxxx/_vti_bin/lists.asmx“;
listService.PreAuthenticate = true;
/*Get Name attribute values (GUIDs) for list and view. */
System.Xml.XmlNode ndListView = listService.GetListAndView(”thelistname”, “”);
string strListID = ndListView.ChildNodes[0].Attributes["Name"].Value;
string strViewID = ndListView.ChildNodes[1].Attributes["Name"].Value;
/*Create an XmlDocument object and construct a Batch element and its attributes. Note that an empty ViewName parameter causes the method to use the default view. */
System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
System.Xml.XmlElement batchElement = doc.CreateElement(”Batch”);
batchElement.SetAttribute(”OnError”, “Continue”);
batchElement.SetAttribute(”ListVersion”, “1″);
batchElement.SetAttribute(”ViewName”, strViewID);
XmlDocument documentQuery = new XmlDocument();
XmlElement query = documentQuery.CreateElement(”Query”);
System.Xml.XmlElement viewFields = documentQuery.CreateElement(”ViewFields”);
// The CAML query to return what I’m looking for.
query.InnerXml = ” <Where>” +
“<Eq>” +
“<FieldRef Name=\”Title\” />” +
“<Value Type=\”Text\”>” + TitleDescription + “</Value>” +
“</Eq>” +
“</Where>”;
//now just get the name of the field you need. this is just an example to guide you