If you look NW from the GCPD, you'll see Ivy's tower on the right, a water tower just to the left of that and on the same section of roof as the water tower but just to the left against a wall, you should see the computer. Hack it.
row 3, Riddle 2
Industrial District - By the Steel Mill's front gate (by where AR training Advanced 1 is) there will be a pay phone next to a building and a man leaning on the pay phone. The man is actually dead. Scan him.