How to call an xml program using the onClick function?

I have a design studio form for RQ44.  We have created an xml screen to display related data associated with the Requisition.  I plan to copy this xml screen and remove some of the none required information.  Then would like to allow the user to click a button that will call the xml screen.

I'm looking for the syntax within the onClick function that will allow me to call the xml screen.

thanks in advance for any help.