Show subwindow below a component

How can I show the subWindow based on component position??

I have a button Logout and want show the "cambiar contraseña" subwindow below it, like profile in gmail.

I am searching the position X & Y of the button but I don´t find it.

I tried using the width of the navigation window (resizable) to locate this position but do not get it.

@SuppressWarnings("serial")
public class ChangePasswordSubwindow extends Window {
	
    public ChangePasswordSubwindow(int positionX, int positionY) {
    	this.setCaption("Cambiar contraseña");
        this.setModal(true);
        this.setDraggable(false);
        this.setResizable(false);
        
        this.setPositionX(positionX);
        this.setPositionY(positionY);
        
        // Configure the windws layout; by default a VerticalLayout
        VerticalLayout layout = (VerticalLayout) this.getContent();
        layout.setMargin(true);
        layout.setSpacing(true);
        
        layout.setSizeUndefined();
    }
}

(...)

ChangePasswordSubwindow changePasswordSubwindow = new ChangePasswordSubwindow(event.getRelativeX(), event.getRelativeY() + 10);
if (changePasswordSubwindow.getParent() != null) {
        // window is already showing
        getWindow().showNotification(
                "La ventana está abierta");
} else {
        // Open the subwindow by adding it to the parent
        // window
      	getWindow().addWindow(changePasswordSubwindow);
}

Any help?

Thanks.