Query on DISPLAY

Hi,
I have a query regarding GUI applications. Not sure, if this is the
correct mailing list, but thought that I could get some
pointers/answers here. Sorry, if this is not the correct mailing list.

I have a daemon which needs to collect some user information, on a
particular event. It has some GTK/Qt based GUI (which is a simple
password collecting dialog). This daemon exposes some APIs, which
applications could use. For a particular API, I need to prompt for a
password from the daemon. I think, the best way would be to exec the
GUI. But I am not sure, where the GUI would appear, when there are
multiple desktops. How do these GUI libraries work?

thanks!
Kala B.