Использование функции DsGetDcName
https://docs.microsoft.com/en-us/windows/desktop/api/dsgetdc/nf-dsgetdc-dsgetdcnamea
C#

//by me :P
using System;
using System.Runtime.InteropServices;
using System.ComponentModel;
using System.Windows.Forms;

namespace dsgetdc
{
    class Program
    {
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        struct DOMAIN_CONTROLLER_INFO
        {
            [MarshalAs(UnmanagedType.LPTStr)]
            public string DomainControllerName;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string DomainControllerAddress;
            public uint DomainControllerAddressType;
            public Guid DomainGuid;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string DomainName;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string DnsForestName;
            public uint Flags;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string DcSiteName;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string ClientSiteName;
        }

        [DllImport("Netapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern int DsGetDcName
          (
            [MarshalAs(UnmanagedType.LPTStr)]
    string ComputerName,
            [MarshalAs(UnmanagedType.LPTStr)]
    string DomainName,
            [In] int DomainGuid,
            [MarshalAs(UnmanagedType.LPTStr)]
    string SiteName,
            [MarshalAs(UnmanagedType.U4)]
    DSGETDCNAME_FLAGS flags,
            out IntPtr pDOMAIN_CONTROLLER_INFO
          );

        [DllImport("Netapi32.dll", SetLastError = true)]
        static extern int NetApiBufferFree(IntPtr Buffer);

        [Flags]
        public enum DSGETDCNAME_FLAGS : uint
        {
            DS_FORCE_REDISCOVERY = 0x00000001,
            DS_DIRECTORY_SERVICE_REQUIRED = 0x00000010,
            DS_DIRECTORY_SERVICE_PREFERRED = 0x00000020,
            DS_GC_SERVER_REQUIRED = 0x00000040,
            DS_PDC_REQUIRED = 0x00000080,
            DS_BACKGROUND_ONLY = 0x00000100,
            DS_IP_REQUIRED = 0x00000200,
            DS_KDC_REQUIRED = 0x00000400,
            DS_TIMESERV_REQUIRED = 0x00000800,
            DS_WRITABLE_REQUIRED = 0x00001000,
            DS_GOOD_TIMESERV_PREFERRED = 0x00002000,
            DS_AVOID_SELF = 0x00004000,
            DS_ONLY_LDAP_NEEDED = 0x00008000,
            DS_IS_FLAT_NAME = 0x00010000,
            DS_IS_DNS_NAME = 0x00020000,
            DS_RETURN_DNS_NAME = 0x40000000,
            DS_RETURN_FLAT_NAME = 0x80000000,
            DS_TRY_NEXTCLOSEST_SITE = 0x00040000
        }

        private static DOMAIN_CONTROLLER_INFO GetDomainInfo()
        {
            DOMAIN_CONTROLLER_INFO domainInfo;
            const int ERROR_SUCCESS = 0;
            IntPtr pDCI = IntPtr.Zero;
            try
            {
                int val = DsGetDcName("", "", 0, "",
                DSGETDCNAME_FLAGS.DS_DIRECTORY_SERVICE_REQUIRED | DSGETDCNAME_FLAGS.DS_FORCE_REDISCOVERY |
                DSGETDCNAME_FLAGS.DS_RETURN_DNS_NAME | DSGETDCNAME_FLAGS.DS_TRY_NEXTCLOSEST_SITE, out pDCI);
                //check return value for error
                if (ERROR_SUCCESS == val)
                {
                    domainInfo = (DOMAIN_CONTROLLER_INFO)Marshal.PtrToStructure(pDCI, typeof(DOMAIN_CONTROLLER_INFO));
                }
                else
                {
                    throw new Win32Exception(val);
                }
            }
            finally
            {
                NetApiBufferFree(pDCI);
            }
            return domainInfo;
        }
        static void Main(string[] args)
        {
            DOMAIN_CONTROLLER_INFO DomainInfo;
            bool ret = true;
            while (ret)
            {
                DomainInfo = GetDomainInfo();
                string msg = "Using API DsGetDcName function with flags:\r\nDS_DIRECTORY_SERVICE_REQUIRED|DS_FORCE_REDISCOVERY|\r\n";
                msg += "DS_RETURN_DNS_NAME|DS_TRY_NEXTCLOSEST_SITE\r\n";
                msg += "===============================================\r\n\r\n";
                msg += "DnsForestName : " + DomainInfo.DnsForestName + "\r\n";
                msg += "DC-Site: " + DomainInfo.DomainControllerName + "\r\n";
                msg += "Client: " + DomainInfo.ClientSiteName + "\r\n\r\n\t TRY AGAIN?";
                MessageBoxButtons buttons = MessageBoxButtons.YesNo;
                if (System.Windows.Forms.MessageBox.Show(msg, "by me :P, 2018, moscoms", buttons) == DialogResult.No)
                    { ret = false; }
            }
        }
    }
}