Usual stuff mate, other than the usual gut feeling about the car and general tidyness/history, the particular talking points I can think right now of a GTI are...
HPFP cam follower, rusting front wings, rusting sills and boot lid badge, diverter valve split, PCV, knocking steering rack on a 2005.
With the DSG wspecially it needs an oil change every 40k so should be due one soon on distance done, check it is smooth. I have a manual but there is info on how to check if the DSG is iffy (can't remember it).
There will be more others chip in with, however they are quite robust cars, if you search for these individually you'll get a better picture.