You can look at the document in <installation>\tools\capture\tclscripts\OrCAD_Capture_TclTk_Extensions.pdf for examples and description. You can also look at samples in <installation>\tools\capture\tclscripts directory.
If you are selecting wire on schematic - see GetSelectedObjects command examples in the document.
Flatnets are calculated by Capture schematic on runtime. Flatnets do not have properties in OrCAD Database. The properties of Flatnets are propogated from the net occurrences. To access the properties at any object see section "3.2.24 Iterate over all effective properties of any object".
Looking at the XML version of the design is one of the best ways to see the structure of the database of your design and to understand which object's property you need to modify to get the desired result. From the TCL command line execute the following command
XMATIC_DSN2XML <DSNFilename> <outputXmlName>
The above command will create an XML output file that shows all the database objects in the design and their relationships.
The document I have mentioned above has examples of TCL iterators that allow you access to any objects in a design. The Effective property examples in the document show you how to modify properties.
If you need further help - you can send your questions to firstname.lastname@example.org