With UI Automation, in general, you have to analyze the target application using the SDK tools (UISpy or Inspect - make sure it's Inspect 7.2.0.0, the one with a tree view). So here for example, when I run notepad, I run inspect and see this:

I see the titlebar is a direct child of the main window, so I can just query the window tree for direct children and use the TitleBar control type as a discriminant because there's no other child of that type beneath the main window.

Here is a sample console app C# code that demonstrate how to get that 'Untitled - Notepad' title. Note the TitleBar also supports the Value pattern but we don't need here because the titlebar's name is also the value.

class Program
{
    static void Main(string[] args)    
    {
        // start our own notepad from scratch
        Process process = Process.Start("notepad.exe");
        // wait for main window to appear
        while(process.MainWindowHandle == IntPtr.Zero)
        {
            Thread.Sleep(100);
            process.Refresh();
        }
        var window = AutomationElement.FromHandle(process.MainWindowHandle);
        Console.WriteLine("window: " + window.Current.Name);

        // note: carefully choose the tree scope for perf reasons
        // try to avoid SubTree although it seems easier...
        var titleBar = window.FindFirst(TreeScope.Children, new PropertyCondition(AutomationElement.ControlTypeProperty, ControlType.TitleBar));
        Console.WriteLine("titleBar: " + titleBar.Current.Name);
    }
}