The Window() function will point to a specific window by the window number or the window name. So, the following will work.
Window( "My Pareto Plot" ) << close window;
But in addition to that, you need to read about name spaces, global variables and local variables.
In short, you can easily declare a Name Space, such as "MySpace", where you can create your window pointers to, and that name space will remain for the duration of your JMP session, unless the name space is specifically modified or deleted. So you can do something like:
nsref = New Namespace( "Myspace" );
Myspace:thePareto = dt << Pareto Plot(……………………..);
Any script that you point to the namespace called "Myspace" will be referencing the same memory variables etc.
Jim