Originally Posted by Cambo

Same day transit in BKK is possible, though this is subject to "rules", where not all airline combo's are allowed for transit. Your flights need to be all on one "ticket", though it is left in the dark (as usual with this), whether the one ticket refers to really one ticket, or one PNR. Upfront verification with the airline (the metal) you fly out of HKG, whether they allow you to check-in/board for their flight is needed. Don't take general statements for granted, get firm statements, if needed, escalate.

You might be able to get a ticket with, for example LH or AY, to obtain a ticket HKG-(Y)-BKK-(J)-(FRA|MUC|HEL)-where-ever-you-go. You won't be able to book that online, though often the airline support desk may be able to book this for you. Always try to get a flight number for the HKG-BKK leg on the airline stock, you fly out of BKK. The factual metal for HKG-BKK won't matter (only for the amount of cabin luggage, mind you, about that !).

Where most people will tell you, that "flying" is not possible (in Asia), that's (bar some exceptions) wrong, just take care to carefully read the instructions for each country, and you'll be able to find solutions. Even solutions that won't cost you a fortune. I've been flying in the past 2 years, without having to pay an extraordinary amount for that, though it needs flexibility, ingenuity and adhering to the rules. And then, it works.

Use ExpertFlyer, Matrix and FR24 to dig deep into the options and get an impression about schedule reliability for each airline/legs. Be aware, airline helpdesks are of no help, in these times, to find solutions. Only when you have your own solutions, they can dive into their systems to book for you.