This was a trip with 4 of us - me, my wife, our daughter who served in HK, and her husband. Several of these have also been recommended by others.
Victoria peak tram
This was fun. Buy tickets in advance. The line to get tickets is really long and the line to take the tram is really long. You only want to wait in one of those lines.
Star ferry
This was fun. It's a ferry ride, but you get a nice view of the surrounding area. We went at night.
Symphony of lights at TST waterfront
This was pretty disappointing. I wouldn't waste time trying to see it again. On the other hand, just walking along the waterfront (and seeing the Bruce Lee statue) is really cool and worth doing.
Fireworks
We happened to be in HK on Hong Kong day and the fireworks were AMAZING! Totally worth standing around for a couple hours with several hundred thousand people.
Hong Kong history museum
It was OK but it was also under construction when we went. If you like museums it could be worth your time.
Wong Tai Sin temple
This was really touristy, but it had some cool statues to see and some cultural exhibits
Diamond hill - Nan Lian garden and Chi Lin nunnery
These two are next to each other. The Nan Lian garden was one of the highlights of the trip for us. It was incredibly beautiful and iirc free.
Big Buddha and the ngong ping tram, the wisdom path, Po Lin monastery
https://www.np360.com.hk/en/explore-np360/nearby-attractions
This was a full day trip iirc. The tram ride out to the big buddha is pretty cool. There is quite a bit to see there and some really short hikes like the wisdom path.
Ladies street in mongkok
This is a street market where you can buy all sorts of random cheap (cost and quality) stuff. It is fun to spend an hour or so here shopping.
Ocean Park
https://www.oceanpark.com.hk/en
This is like Hong Kong's Lagoon, but the rides are not as nice as Lagoon's. It was OK. There are some animal exhibits like penguins and fish. The highlight might be the Giant Pandas and Red Pandas.
Tsz Shan Monastery
TszshanThe idea for the development of Tsz Shan Monastery germinated with Mr. Li Ka-shing. From a young age, Mr. Li was influenced by his elders, and had developed a life-long affinity with Buddhism. In 1980, Mr. Li established a personal foundation to cultivate a culture of giving, and has since pledged...
https://www.tszshan.org/home/new/en/visit.php#guide#guide[https://www.tszshan.org/home/new/en/visit.php#guide]
This was a very beautiful monastary. There is a museum there that is also really cool.
Stanley Market
Another place where you can do some great souvenir shopping. This has actual stores though rather than being a street market like Ladies street.
Another must-do is to buy a pineapple bun (bolo bao) from a bakery each morning when they are fresh and warm. They do not taste like pineapple but look vaguely like pineapple. But they are VERY tasty!
Feel free to dm me if you have any specific questions