Novel Research
The following (current) flights operate between Narita (NRT) and HKG at the times you have stated for your book: CX505 18.20/22.35, JL 735 18.25/22.30, NH911 (appropriate?) 18.40/22.50. NH911 is code shared with NW11.
The passenger could transfer on arrival in HKG and be flying out to MAD or BCN via a range of places. You cannot fly direct to MAD or BCN however the "most direct" would be via Rome (FCO). Other options would be via London (LHR), Amersterdam (AMS), Paris (CDG) etc.... Let me know if you want to get more specific with timings and locations.
The passenger could have used the inflight phone if it had not been disabled. Other than that there would not be a way of knowing (overhearing a conversation between aircrew/cabin crew but this would be unlikely given the circumstances). In reality the cockpit crew probably would not have heard until they arrived in HKG. Conversations that I have had with people flying in HKG at the time said that they didn't know for sometime after they landed from the flight that they were on.
Let me know if you need any additional info.