Programs that use GWM (usually via a graphics package such as GKS or IDI) will normally create a
new window as required. However, to plot into an existing window you need to know how the
graphics package generates the window name. For example, GKS uses a window with the name
GKS_nnnn where nnnn is the workstation type (the connection identifier is ignored) or whatever that
name translates to if treated as an environment variable.
Consult the documentation for the graphics package in question for full details.