No real significant issues that will stand out. The HPFP/CP4 issues is what you will read horror stories about but it's not as common as it may seem on the interwebs. I really love the 2.0 CR motor, when stock its quieter than enough gas cars. Torque peaks around 1700-1800rpm so its a lot of fun to drive. Has good power overall and gets very good fuel efficiency.
I haven't followed if the DSG still suffers the occasional DMF failure or mechatronics issue from time to time. On the earlier MKV's they did.
Something to note about the Sportwagen, you may get confused reading around about them. Why VW called it the Jetta Sportwagen makes no sense, its a Golf not a Jetta. It shares the MKVI Golf platform which shared a lot with the MKV Jetta. The MKVI Jetta came in 2011 and the MKVII Golf came in 2013. These two officially break the shared platform between the Golf and Jetta. For 2015 the Jetta Sportwagen chose to stick with the Golf Platform and will finally be called by its real name. Whats important to know is that a 2012 Sportwagen will not share many things with the 2012 Jetta. Obviously some stuff will, but my point is that it is not simply a Jetta hatchback.
Personally I do not like the MKVI Jetta's one bit. The outside is okay, but they dumbed them down and cheapened them up so much inside for the NA market that its depressing. The good news is the Sportwagen still has the luxurious feel of the older ones.
Theres a ton of VW forums that would have more info. Overall, I wouldn't worry about anything with that car. Fairly reliable as VW's tend to be overall, however you do pay German price when you go to fix them. At the same time, the replacement parts tend to be high quality so you do get what you pay for more so than with some others.
They do have a DPF on them, but you can fix that. Leave the stock muffler on and its still very very quiet, its a bit loud straight piped. Here's a couple videos of the TDI Cup edition my wife drives. With her driving it gets 45mpg+ and she's not a slow driver. 6 speed manual. Exhaust is a rawtek downpipe/midpipe with borla rear. Tuning is Malone Stage 2. Can't say it really gained a lot of MPG's with the delete/tune, but definatley gained some power and is fun to drive.
https://www.youtube.com/watch?v=Cn4YAMx6sxQ
Without muffler.
https://www.youtube.com/watch?v=n5Ns2Kqp-Mo