using System;

using System.Collections.Generic;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        var json = "[{\"tipo\":\"simnao\",\"pergunta\":\"rwerw#erwerewr ?\",\"tag\":\"#acimadopeso\",\"resposta\":\"\",\"$$hashkey\":\"object:410\"},{\"pergunta\":\"werwerwerwer ?\",\"tag\":\"#diabetes\",\"resposta\":\"\",\"$$hashkey\":\"object:412\"},{\"pergunta\":\"werwerwer ?\",\"tag\":\"#idoso\",\"resposta\":\"\",\"$$hashkey\":\"object:414\"}]";     

        JArray array = JArray.Parse(json);      

        var tags = new List<string>();      

        foreach (var a in array)

            tags.Add(a["tag"].ToString());

        tags.ForEach(x => Console.WriteLine(x));

    }

}