Your code has two problems. One, SSN must be static if your going to use it in the Main method. Two, Console.WriteLine("{0},SSN") should be Console.WriteLine("{0}", SSN).
namespace ConsoleApplication6
{
    class Program
    {
        public static string SSN { get; set; }
        // Return a hash code based on a point of unique string data.
        public override int GetHashCode()
        {
            return SSN.GetHashCode();
        }
        public static void Main(string[] args)
        {
            Console.WriteLine("{0}", SSN);
        }
    }
}
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solved Unable to access property in C# in Main() [closed]