In my previous post, https://realmpksharepoint.wordpress.com/2014/04/01/get-all-the-webparts-of-a-sharepoint-webpage-using-client-object-model-c/ , I have explained how to get WebParts properties. Now, if you’re interested in getting the schemaXml of that WebPart (like exporting a WebPart from the SharePoint Page in edit mode) then you can’t do that using CSOM. Here, the only available solution is the WebService, WebPartPages.asmx. You can view all the functions of this WebService at the url, YourSiteUrl/_vti_bin/WebPartPages.asmx.

What I am going to use here, is the method, GetWebPart2. This method takes three parameters, complete page Url, WebPartGuid, behavior-Shared/User.

string webPartInfo = String.Empty; 
string webServiceUrl = ctx.Web.Url + "/_vti_bin/WebPartPages.asmx";

//GetCompleteUrl is a custom utility function to append the web url and page //serverRelativeUrl.
string pageUrl = Utility.GetCompleteUrl(ctx.Web.Url, pageServerRelativeUrl);

StringBuilder sbEnvelope = new StringBuilder();

sbEnvelope.Append("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
sbEnvelope.Append("<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">");

sbEnvelope.Append(String.Format(
"<soap:Body>" +
    "<GetWebPart2 xmlns=\"http://microsoft.com/sharepoint/webpartpages\">" +
        "<pageurl>{0}</pageurl>" +
        "<storageKey>{1}</storageKey>" +
        "<storage>{2}</storage>" +
        "<behavior>Version3</behavior>" +
    "</GetWebPart2>" +
"</soap:Body>"
, pageUrl, storageKey, "Shared"));
sbEnvelope.Append("</soap:Envelope>");

HttpWebRequest req = (HttpWebRequest)WebRequest.Create(webServiceUrl);
req.Method = "POST";
req.ContentType = "text/xml; charset=\"utf-8\"";
req.Accept = "text/xml";
req.Headers.Add("SOAPAction", "\"http://microsoft.com/sharepoint/webpartpages/GetWebPart2\"");
req.UseDefaultCredentials = false;

Uri targetSite = new Uri(ctx.Web.Url);
SharePointOnlineCredentials spCredentials = (SharePointOnlineCredentials)ctx.Credentials;

string authCookieValue = spCredentials.GetAuthenticationCookie(targetSite);
req.CookieContainer = new CookieContainer();
req.CookieContainer.Add(
    new Cookie("FedAuth",
        authCookieValue.TrimStart("SPOIDCRL=".ToCharArray()),
        String.Empty,
        targetSite.Authority));

using (Stream stream = req.GetRequestStream())
{
    using (StreamWriter writer = new StreamWriter(stream))
    {
        writer.Write(sbEnvelope.ToString());
    }
}

WebResponse response = req.GetResponse();
Stream responseStream = response.GetResponseStream();

XmlDocument xDoc = new XmlDocument();
xDoc.Load(responseStream);

if (xDoc.DocumentElement != null && xDoc.DocumentElement.InnerText.Length > 0)
    webPartInfo = xDoc.DocumentElement.InnerText;

//webPartInfo is your WebParts SchemaXml.