In reply to Caprid: https://hongkongclimbing.com/ has much of the information you'll need.
Plenty of granite bouldering, but for much of that you would want a pad. Ideally, bring a harness + rope and try to hook up with some locals and head to Tung Lung island for a memorable day out or multipitch it up Lion Rock (Kowloon) -- something I've wanted to do but still not managed in all the years I've been going!
Most places are easy to get to with some MTR and taxi, and a local to get you to the crag. There is some sharp vegetation about and possibly need to hack it if going to some lesser used bouldering spots. The main climbing areas should have easy access (other than the need for a ferry or MTR/taxi).
Had an 18 hour layover in HK about a month ago and got to climb a quick multi-pitch on Lion Rock (Gweilo to Wards Grooves). Quite nice and a pretty unique setting - a dense jungle complete with monkeys overlooking a metropolis of 7 million people. Granite was a little greasy but the dim sum was to die for.