Lastly, please note that you'll always need to show your Valid Passport, or a Photocopy of it, when purchasing or picking up train tickets. You cannot pick up tickets for other people if they are not present.
And it is especially important to note that most high-speed trains end services around 9-10pm. If you've ever missed the train returning from Shanghai, for instance, they usually have slow trains that will take you to Kunshan Railway Station until about 12am. So if you've missed the last high-speed train in another city, try going to their Railway station and see if slow trains to Kunshan are available.
Kunshan Railway Station Address: No.1 Renmin South Rd. Kunshan