Originally Posted by
prathetkrungthep
Now assuming that JFK-HND-PVG is on JL metal, he could try to OLCI via JL's website. I don't see why that wouldn't work. If it doesn't work for some reason, then he should leave the secure area to check-in at the JL desk. Theoretically JL agents at the gate should be able to check him in, but I don't know if they will appear at the gate early enough before the flight closes.
The JAL agents will typically move from check in to the gate. There will be no one at the gate until past check in time. There is usually a JAL staff member in the lounges that can help with various matters, can't say for sure for New York, but in other US gateways it is the case. But then comes the question, does the traveler have lounge access.