string json = @"[{""Id"":100832502,""Sku"":""4056567444463"",""QuantityOnHand"":2,""Warehouses"":[{""ProductId"":100832502.0,""WarehouseId"":32687.0,""QuantityOnHand"":2.0,""WarehouseSKU"":""4056567444463"",""IsActive"":true,""IncludeInSyncBalance"":true}]}]";
    


   var Item = JsonConvert.DeserializeObject<List<RootObject>>(json);

 Response.Write(Item[0].Warehouses[0].QuantityOnHand.ToString());

        public class Warehouse
        {
            public double ProductId { get; set; }
            public double WarehouseId { get; set; }
            public double QuantityOnHand { get; set; }
            public string WarehouseSKU { get; set; }
            public bool IsActive { get; set; }
            public bool IncludeInSyncBalance { get; set; }
        }

        public class RootObject
        {
            public int Id { get; set; }
            public string Sku { get; set; }
            public int QuantityOnHand { get; set; }
            public List<Warehouse> Warehouses { get; set; }
        }