You can find a comprehensive listing of group codes in the AutoCAD help system. Here are instructions for finding the Tables section group codes.
1. In AutoCAD, choose Help > AutoCAD Help from the menubar
2. Click on the Contents tab of the Help Topics dialog box, then double click Customization Guide
3. Double click on DXF Reference then again on Shortcut to DXF Reference
4. At the AutoCAD Visual LISP and ActiveX Help dialog box, double click on DXF Reference.
5. Double click on Chapter 4: TABLES Section.
You will see a listing of group code topics. Click on the button next to the topic you are interested in.