I'd suggest you think this through first.
There have been reports of "onlookers" -- including at least one Westerner -- being arrested.
Crowds move quickly and unexpectedly, and can suddenly put you where you don't really want to be.
If you spend any time in Hong Kong or the Mainland, you should assume your face will be scanned and that this may have consequences.
Up to you, but I myself don't think viewing the protests as some sort of tourist spectacle is a good idea.
Nothing illegal about observing things for yourself. Avoid areas that are too packed, avoid the frontline and the police, and you'll be fine. If you're white, you'll be extra fine. Also, don't wear white/black t-shirts. (Especially not white.)
I went to one of the protests to see it for myself. It's an important piece of history and I think people who see it with their own eyes will be glad they did.