using WhoisObserver;
using WhoisObserver.Services.Model;
...

async void Test1()
{
    var st0 = new WhoisClient();
    var st1 = st0.GetResponceJsonAsync("ya.ru", ServersClientFamily.IpApi).Result;
    Console.WriteLine(st1.CountryCode);
}

Test1();

using WhoisObserver;
using WhoisObserver.Services.Model;
...

async void Test2()
{
    var st0 = new WhoisClient();
    var st1 = st0.GetResponceModelAsync("13.228.116.142", ServersClientFamily.IpApi).Result;
    Console.WriteLine(st1.CountryCode);
}

Test2());