Код выглядит следующим образом:

Часы:

public class Clock
{
    public event Func<DateTime, bool> SecondChange;

    public void Run()
    {
        for (var i = 0; i < 20; i++)
        {
            Thread.Sleep(1000);

            if (SecondChange != null)
            {
                //how do I get return value for each subscriber?
                Console.WriteLine(SecondChange(DateTime.Now));
            }
        }
    }
}

DisplayClock:

public class DisplayClock
{
    public static bool TimeHasChanged(DateTime now)
    {
        Console.WriteLine(now.ToShortTimeString() + " Display");
        return true;
    }
}

LogClock:

public class LogClock
{
    public static bool WriteLogEntry(DateTime now)
    {
        Console.WriteLine(now.ToShortTimeString() + " Log");
        return false;
    }
}

Чтобы запустить код:

var theClock = new Clock();
theClock.SecondChange += DisplayClock.TimeHasChanged;
theClock.SecondChange += LogClock.WriteLogEntry;
theClock.Run();

The other questions are:

Is it good practice for each subscriber to return a value? Is it good practice to just declare Action/Func as the event return type instead of manually declaring a delegate?