using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var data = new List<int>();

        var iterator = data.Where(x => 1 == 1);

        var type = iterator.GetType();

        var sourceField = type.GetField("source", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

        Console.WriteLine(sourceField.FieldType);

    }

}