How to iterate through window elements using JNA?

Using JNA, my ultimate goal is to read a message that was sent using Windows NET SEND or MSG.EXE, which appears as a Windows pop-up message window on the receiving machine.

I am already able to search for this specific message window and get the hWnd handle using the code below. My problem now is how to I iterate through all the elements of this window to find the actual message text, read the message, and also click the OK button?

My research tells me I need to use FindWindowEx (to go through the elements) and PostMessage (to click the OK button) but I am struggling to make it work.

package democode;

import com.sun.jna.Pointer;
import com.sun.jna.Native;
import com.sun.jna.win32.StdCallLibrary;

public class JNA_Main {
    // Equivalent JNA mappings
    public interface User32 extends StdCallLibrary {
    User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class);

    interface WNDENUMPROC extends StdCallCallback {
        boolean callback(Pointer hWnd, Pointer arg);
    }

    boolean EnumWindows(WNDENUMPROC lpEnumFunc, Pointer arg);

    boolean PostMessage(Pointer hwndParent, String msg, String wParam, String lParam);
    Pointer FindWindowEx(Pointer hwndParent, String hwndChildAfter, String lpszClass, String lpszWindow);

    int GetWindowTextA(Pointer hWnd, byte[] lpString, int nMaxCount);

    }

    public static void main(String[] args) {
    final User32 user32 = User32.INSTANCE;

    user32.EnumWindows(new User32.WNDENUMPROC() {

        int count;

        public boolean callback(Pointer hWnd, Pointer userData) {
        byte[] windowText = new byte[512];
        user32.GetWindowTextA(hWnd, windowText, 512);
        String wText = Native.toString(windowText);
        wText = (wText.isEmpty()) ? "" : "; text: " + wText;

        if (wText.contains("My Window Name")){
            System.out.println("Found window " + hWnd + ", total " + ++count + wText);

            //**************************************************//
            //NEED CODE HERE TO ITERATE THROUGH ELEMENTS OF THIS PARTICULAR WINDOW, READ THE MESSAGE TEXT AND CLICK OK BUTTON.
            //**************************************************//

        }

        return true;
        }
    }, null);
    }
}

The logical choice via the MSDN is to call EnumChildWindows using the hWnd pointer that you've received from the callback method above.