watch on something
watch over something

He turned back to watch their effect on the girl.

You watch here on the other side of the room.

Can anyone really know who is watching what on television?

We've been watching you on the news every day now.

So how come I can still watch almost every video on the site?

And why did they want to watch things on television?

When you watch it on film, everybody is running hard.

But he went outside to watch the fire on the hill.

I thought we were going to be able to watch it on line.

Now, why don't you get back home and watch the whole thing on television.