I have not specifically transferred to a 5J flight from HKG, but should operate the same way from other airports. Cebu Pacific is an LCC and for the most part, point-to-point only, although there are exceptions. They claimed they formed the Vanilla Alliance but I have yet to see any other codeshare on their website aside from TigerAir (Cebgo is their own brand, so doesn't really count). Since there is no Cebu Pacific transfer desks airside at HKG, you have to go through immigration and check in from their bag drop counter landside, even if you do not have any baggage. That is the only way they can confirm you have necessary documents to travel internationally to your destination. However, note that Cebu Pacific is also very strict with carry on items. Your carry on must weigh less than 7 kg. You can exclude "personal items", but Cebu Pacific is known for strictly enforcing this weight limit and forcing passengers to pay baggage fees. I often see them weigh people's carry-on and the maximum weight I have seen them let people through is 10 kg (7 kg to 10 kg is the gray area); above that, their policy is to slap those baggage fees.