using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Security.Claims;
using System.Web.Http;
using System.Web.Http.Results;

namespace DoctorWebService.Controllers
{
    public class DataController : ApiController
    {
        [Authorize]
        [HttpGet]
        [Route("api/doctors")]
        public JsonResult<object> Get(string doctorCode)
        {
            if (doctorCode == "666")
            {
                var identity = (ClaimsIdentity)User.Identity;
                return Json<object>(new
                {
                    stampCode = "666",
                    email = "666_doctor@gmail.com",
                    phone = "+370 640 000000",
                    healthCareProvider = "Jonavos poliklinika"
                });
            }
            else
            {
                return Json<object>(new
                {
                    notFound = 0
                });
            }
        }
    }
}

it returns:

{
  "stampCode": "666",
  "email": "666_doctor@gmail.com",
  "phone": "+370 640 000000",
  "healthCareProvider": "Jonavos poliklinika"
}

[
  {
    "stampCode": "666",
    "email": "666_doctor@gmail.com",
    "phone": "+370 640 000000",
    "healthCareProvider": "Jonavos poliklinika"
  }
]

[
  "stampCode: 666",
  "email: 666_doctor@gmail.com",
  "phone: +370 640 000000",
  "healthCareProvider: Jonavos poliklinika"
]