Niobe is the drug pusher in the sewer. From Dream city map, tap drug icon to climb down to the sewer. Niobe wears red jacket so it should be easy to find her.
Hi, from where did you know about Niobe? You will not know about her name unless you already talk to her in the sewer. The game through checklist screen will ask you to find a drug pusher in the sewer. If you climb down to the sewer, you'll meet a female with red jacket. Talk to her & then you'll know she's Niobe. The person with blue jacket is just a drug addict. He doesn't serve any important role. You can ignore him.