This is the second of the Riddlers trials accessed after visiting the orphanage.
Head to the marker underneath Chinatown and go down the lift.
The aim is to get your batmobile to the power socket so you can power the board up.
As batman, you need to stand on the pressure plate above the entrance that controls the middle ledge. Stay here the whole trial.
Equip your remote batmobile, and follow the circuit. Use B to put ledges in/out.
You can rest ramps on top of ledges (also) controlled by B so you can make the jumps.
Once you get to the end, simply power the socket up.
The board will then light a pattern, with one light indicating the key. Switch to catwoman, and open the correct key cabinet. You need to look at the layout on the board and select the correct key. For me, it was the bottom left light.