class Program
{
  static void Main()
  {
    var barInfo = typeof(Zot).GetMethod("Bar",
      BindingFlags.Instance | BindingFlags.Public, null, new [] {typeof(string), typeof(object[])}, null
    ) ?? throw new ApplicationException("Method Bar notfound");
    foreach (var i in typeof(Zot).GetInterfaces())
    {
      var map = typeof(Zot).GetInterfaceMap(i);
      var index = Array.IndexOf(map.TargetMethods, barInfo);
      if (index==-1) continue;
      var interfaceMethod = map.InterfaceMethods[index];
      Console.WriteLine(((DescriptionAttribute)Attribute.GetCustomAttribute(interfaceMethod,
         typeof(DescriptionAttribute))).Description);
    }
    Console.WriteLine("done");
    Console.ReadKey(true);
  }
}

public interface IFoo
{
  void Bar();
  void Bar(int t);
  void Bar(DateTime dt);

  [Description("huh?")]
  string Bar(string s, params object[] args);
}

public class Foo : IFoo
{
  public virtual void Bar()
  {
    throw new NotImplementedException();
  }

  public virtual void Bar(int t)
  {
    throw new NotImplementedException();
  }

  public virtual void Bar(DateTime dt)
  {
    throw new NotImplementedException();
  }

  public virtual string Bar(string s, params object[] args)
  {
    throw new NotImplementedException();
  }
}

public class Zot : Foo { }