The Natural Construct Generation section of the documentation describes the generation wizards. http://techcommunity.softwareag.com/ecosystem/documentation/naturalONE/natONE911/cgen/n1codegeneration/cst-generation.htm
The procedure for each wizard ends with text similar to
And here is where to read about the user exits.
http://techcommunity.softwareag.com/ecosystem/documentation/naturalONE/natONE911/cgen/n1codegeneration/defining-user-exits.htm#defining-user-exits