There are multiple ways to open the Postprocessing window. You can:
Select from the Windows Start menu.
Right-click a Postprocessing node on the Scenery pane and select .
Start optiSLang with the command line or in batch mode.
Start the postprocessing executable from a command line.
Use a Python command script, for example add_custom_data_plot.py.
Note: Many wizards and nodes also provide options that open postprocessing automatically.