After cleaning up the crime scene (or not), leave the diner. Walk across the street (towards the screen) and to the right and eventually the camera angle will change and show you the subway entrance. Walk down the stairs to pop the trophy.
I recommend doing this one via chapter select, especially if you're trying to get everything in a single playthrough.
Dine and Dash requires you to use the taxi instead of the subway, and there's no pay-off for setting up Lucas' escape via subway.
Solution taken from PlayStation Trophies:
https://www.playstationtrophies.org/game/indigo-prophecy/tro...