using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        string name = "HelloWorld";

        string birthdate = "2020-03-03";

        string birthplace= "Nowhere";

        var jsonData = JsonConvert.SerializeObject(new

        {

            Data = $"\"Name\"=\"{name}\",\"BirthDate\"=\"{birthdate}\",\"BirthPlace\"=\"{birthplace}\""

        });

​

        Console.WriteLine(jsonData);

    }

}