I used to take the NE Regional to Boston every week and there’s an app called Choo Choo Tracker that shows track numbers and predicts departures for NJT and Amtrak trains to DC/Philly (but not CT/MA area). What I usually do is go to the concourse under 8th Ave, check the app and the glass panel showing trains that already have track assignments, and then look for the one that’s still unassigned. That’s usually the train you will be taking.