<?xml version="1.0" encoding="UTF-8"?><Test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><a>0</a><s>мама мыла раму</s><d>0001-01-01T00:00:00</d><_innerTest><b>10</b></_innerTest></Test>

OracleCommand oraCmd = new OracleCommand("insert into test (xmldoc) values (:xmlDoc)", oracon);

            oraCmd.Parameters.Add(new OracleParameter("xmlDoc", OracleDbType.XmlType, new OracleXmlType(oracon, xmlDoc), ParameterDirection.Input));

            oraCmd.ExecuteNonQuery();

            OracleCommand oraCmd = new OracleCommand("select xmldoc from test", oracon);
            

            OracleDataReader oraReader = oraCmd.ExecuteReader();
 
            
            while (oraReader.Read())
            {
                xmlDoc = oraReader.GetOracleXmlType(0).GetXmlDocument();
            }

  <?xml version="1.0" encoding="UTF-8" ?> 
- <Test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <a>0</a> 
  <s>мама мила раму</s> 
  <d>0001-01-01T00:00:00</d> 
- <_innerTest>
  <b>10</b> 
  </_innerTest>
  </Test>

select t.xmldoc.getclobval() xmldoc from test t

OracleCommand oraCmd = new OracleCommand("select new XMLTYPE(convert( test.xmldoc, 'UTF8', 'UTF8')) from test", oracon)

 xmlDoc = oraReader.GetOracleXmlType(0).GetXmlDocument();