What to do when suture becomes exposed behind the ear following ear "tucking"/"pinning" cosmetic surgery? (photos)

This sounds like a extruded suture with granulation tissue surrounding it.  I would recommend you see someone to be evaluated, but seems like all that is required is to remove the suture.  This should heal fine.

Suture exposure is not unusual following otoplasty, since permanent sutures are used for the reconstruction. 12 years following surgery is certainly safe to remove that suture that is exposed. Your reconstruction is no longer dependent upon the sutures for stability. Seek consultation with your surgeon or another surgeon experienced in ear reconstruction to remove that exposed suture. After removal, you should have resolution of symptoms and it should heal quickly.Good luck!

The photographs are not in focus so it is not possible to comment on the images.It is certainly possible for a stitch to come to the surface years after a pinnaplasty. It is standard practice to use non dissolving stitches. These can usually be easily removed possibly with some local anaesthetic. I advise you to consult a suitably qualified and experienced plastic surgeon who will be able to advise you.

The exposed suture should be removed at this time, with no adverse consequences expected. It is a common occurence after this surgery.