از HtppContext.Current استفاده کنید و بعد Request را میتونید بگیرید

using System;
using System.Collections.Generic;
using System.Net;
using System.Text;
using System.Web;
using System.Text.RegularExpressions;
 
namespace forgetcode
{
    class Program
    {
        static void Main(string[] args)
        {
           
             Uri referrer = HttpContext.Current.Request.UrlReferrer;
            if (referrer != null)
            {
                string original = referrer.OriginalString.ToLower();
                Console.WriteLine("Visitor Came From "+original);
            }
        }
       
     }
}