Originally Posted by Rain187

First, I assume your flight is with CX and the check-in/ boarding procedure at JFK shall be done by the CX staff who will determine if your bag is "small enough" to comply with the hand baggage, if it doesnt comply, they will check-in the baggage at the gate for you and it shall be a through check in to SIN.

If the staff at JFK let you take the hand baggage on board and the CX staff at HKG reject you, they will do the same thing, check-in the baggage at gate for you. There is no need to go to the landside and technically it is not feasible now due to the COVID-19 measure. All passenger enter HK need to go through all those COVID-19 testing procedure (which take hours) and then quarantine for 7 days/ 14 days or 21 days in a hotel which means you will miss your connecting flight for sure. Of coz this policy subject to change based on the Government Policy and the pandemic situation and it is hardly to say now.