using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var json = @"{ ""data"": [[1,2,3],[4,5,6],[7,8,9]]}";

        var obj = JsonConvert.DeserializeObject<Container>(json);

        obj.Dump();

    }

    public class Container

    {

        public double[][] Data { get; set; }

    }

}