Correct...at SIN. At HKG, a *G travelling on a Star Alliance carrier can get into the SilverKris lounge in any class of service.

If OP has time at HKG, they can start with the SQ lounge since it's closest to exit immigration. But it doesn't have any windows so it can feel cramped. If that's not to their liking, then head to the AmEx lounge, which in my opinion is the best option, but I've found it difficult to get a good seat due to crowding. I actually like the UA lounge. It's more open than SQ, food/drink isn't bad, and seems spacious even during the time prior to mid-day UA departures. There's also a TG lounge nearby, but I've never tried it.