Just answering for the "into HKG" part of the question.

Assuming this is a direct flight from Europe (all bets are off if you connect somewhere else, obviously) and that the flight path is similar to that for LHR-HKG, probably right for a closer look at the city, but left probably gets you a decent view from farther out. It appears that the most common approach passes by the city and then loops back.

However, at least some of the time the approach is more direct, in which case you may be able to see more looking forward out of the left side of the plane.

Just answering for the "into HKG" part of the question.

Assuming this is a direct flight from Europe (all bets are off if you connect somewhere else, obviously) and that the flight path is similar to that for LHR-HKG, probably left for a closer look at the city. It appears that the most common approach passes by the city and then loops back.

However, at least some of the time the approach is more direct, in which case you may be able to see more looking forward out of the right side of the plane.