As a general rule, tipping in HK is not required, but it will be welcomed if the service is excellent.
For tipping in restaurant, 3% to 5% tip is already very good. I was reminded many times by my friends there: you guys from US are tipping too much. 10% is a lot of tips by HK standard.
In Japan, tipping sometimes is considered as insult. So consult the locals first before you tip.