using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

​

        string json = "[{\"skuId\":\"1234\",\"plans\":[{\"plan\":{\"planName\":\"plan1\",\"planId\":\"abcd1231\"}},{\"plan\":{\"planName\":\"plan2\",\"planId\":\"loks3123\"}}]},{\"skuId\":\"5341\",\"plans\":[{\"plan\":{\"planName\":\"plan3\",\"planId\":\"awer3234\"}},{\"plan\":{\"planName\":\"plan4\",\"planId\":\"gefd4231\"}}]},{\"skuId\":\"7649\",\"plans\":[{\"plan\":{\"planName\":\"plan5\",\"planId\":\"kitv5397\"}}]}]";

        JToken obj = JToken.Parse(json);

        string id = (string)obj.SelectToken("$..[?(@.plans[*].plan.planId == 'loks3123')].skuId");

        Console.WriteLine("Sku Id : " + id);

    }

}

public class Account

{

    public string Email { get; set; }

    public bool Active { get; set; }

    public DateTime CreatedDate { get; set; }

    public IList<string> Roles { get; set; }

}

​