The Şükrü Saracoğlu Stadium is in Kadıköy on the Asian side, easily walkable from the ferry 15 mins or so, just follow the crowds in blue and yellow. The ferries goes from Eminönü, Karaköy (either side of the Galata bridge) or Besiktaş. If he's on the Asian side get the train to Söğütlüçesme.
Don't go in the end stands (numaralı

he'll want to be in the Maraton or Migros Tribünü stands, as in England comparing prices is an indication of personal safety. Tickets are normally available in advance from a number of outlets, including the club shops, but I don't know about Champions League games.
Traffic and travelling will be a nightmare, not as bad as the Olympic Stadium, but leave pleanty of time. Everywhere in the ground will be noisy and carries some risk, flares, guns, knives, as well as ordinary decent violence. It is probably safest to be Fenerli for the night, not neutral saying "I just want a good game of football" and if they ask who he supports in England say Stoke or Watford or something similar.