<?php
require_once('./lib/nusoap.php');
$str_URL = "http://localhost/nusoap/index.php";
$str_namespace = $str_URL . '?wsdl';

$obj_server = new soap_server();
$obj_server->soap_defencoding = 'utf-8';
$obj_server->decode_utf8 = false;
$obj_server->encode_utf8 = true;
$obj_server->configureWSDL('books', $str_namespace);
$obj_server->register('get_data', array(),
                  array('return'=>'xsd:string'));

function get_data() {
  $arr_data = array(
    array('id'=>'1', 'isbn'=>'aaa', 'author'=>'bbb', 'year'=>'2020'),
    array('id'=>'2', 'isbn'=>'bbb', 'author'=>'ccc', 'year'=>'2020')
  );
  $obj_xml = new DOMDocument('1.0', 'utf-8');
  $obj_xml_item = $obj_xml->createElement('items');
  foreach($arr_data as $arr_d) {
    $obj_xml_subitem = $obj_xml->createElement('item');
    foreach($arr_d as $k => $v) 
      $obj_xml_subitem->setAttribute($k, $v);

    $obj_xml_item->appendChild($obj_xml_subitem);
  }
  $obj_xml->appendChild($obj_xml_item);

  return $obj_xml->saveXML();
}

$POST_DATA = isset($GLOBALS['HTTP_RAW_POST_DATA']) 
                ? $GLOBALS['HTTP_RAW_POST_DATA'] : '';

$obj_server->service($POST_DATA);
?>

using System;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void bnCallWSDL_Click(object sender, EventArgs e)
        {
            try
            {
                ServiceReference1.booksPortTypeClient bc = new ServiceReference1.booksPortTypeClient(); // NuSOAP
                String data = bc.get_data(); // Возвращает XML
                MessageBox.Show(data); // Показываем Alert
                DataSet ds = new DataSet(); 
                DataTable dt = new DataTable("tb1");
                dt.Columns.Add("id");
                dt.Columns.Add("isbn");
                dt.Columns.Add("author");
                dt.Columns.Add("year");
                ds.Tables.Add(dt);

                StringReader sr = new StringReader(data);
                ds.ReadXml(sr, XmlReadMode.ReadSchema);
                this.dataGridView1.DataSource = ds.Tables[0];
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
       }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}

$obj_server->soap_defencoding = 'utf-8';
$obj_server->decode_utf8 = false;
$obj_server->encode_utf8 = true;