WorkstationIdReader

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Win32;

namespace WorkstationId
{
    class Program
    {
        static void Main(string[] args)
        {
            var path = @"SOFTWARE\Citrix\ICA\Session\ClientName";
            var id   = RegistryHelper.GetValue(path);
            Console.WriteLine("WorktationId: " + id);
            Console.ReadLine();
        }
    }

    public static class RegistryHelper
    {
        // GetValue searches both the 32-bit and 64-bit views in the registry
        public static string GetValue(string registryPath)
        {
            var lastSlashIndex = registryPath.LastIndexOf("\\");
            var keyName        = registryPath.Substring(0, lastSlashIndex);
            var valueName      = registryPath.Substring(lastSlashIndex + 1);

            var key = Registry.LocalMachine.OpenSubKey(keyName, RegistryKeyPermissionCheck.ReadSubTree);
            if (key == null)
            {
                Console.WriteLine("Registry64");
                var hklm64 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
                key = hklm64.OpenSubKey(keyName, RegistryKeyPermissionCheck.ReadSubTree);
            }
            else
            {
                Console.WriteLine("Registry.LocalMachine.OpenSubKey");
            }

            if (key == null)
            {
                Console.WriteLine("Registry32");
                var hklm32 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32);
                key = hklm32.OpenSubKey(keyName, RegistryKeyPermissionCheck.ReadSubTree);
            }

            if (key != null)
            {
                var workstationId = key.GetValue(valueName);
                if (!string.IsNullOrWhiteSpace(workstationId?.ToString()))
                {
                    return workstationId.ToString();
                }
            }

            return null;
        }
    }
}