If I understand this correctly you have a  JDesktopPane which contains
a JInternalFrame "Student".

If the user is on the "Student"  JInternalFrame - you want them to be
able to click on a button and opens the "Course" JInternalFrame.    Is
that correct?

The following is pseudo code which will do that .... this will add a
JInternalFrame to the same JDesktopPane as an existing frame.

......  from inside a class which derives JInternalFrame......

   JDesktopPane  mycontainer = this.getDesktopPane();
   mycontainer.add( new MyCustomerJInternalFrame("Course") );

If you suspect the "Course"  JInternalFrame is already open - you can
find it using....

   JDesktopPane  mycontainer = this.getDesktopPane();
   JInternalFrame[] frames = mycontainer.getAllFrames();
   for ( int i = 0; i < frames.length; i ++ ) {
        if ( frames[i].getTitle().equals("Course") ) {
              // that's it
        }
   }

Jay