How can I drill a hole in a china bathroom sink to add a soap dispenser?
You could try a carbide hole saw, but don't be at all surprised when you break the sink. Porcelain does not take well to cutting or grinding.
I will be very surprised if you can accomplish cutting a hole in a china sink. But I could be wrong. So if you should get this done please post back as how you did it.
It this a wall-mount sink? Much easier would be to go through the countertop if it's got one. If not, save yourself the trouble and just use a wall-mount soap dispenser. There's a lot of nice ones available.