How do I stop this person (IP address) from trying to connect to my Mac via screensharing?
The bigger question here is why is your Mac not behind a firewall that is doing some sort of port filtering/forwarding as well as stateful packet inspection?

If you were behind a firewall you could block/filter out IP addresses, but this is only temporary because all the attacker has to do is change their IP.

Instead of VNC, which in my opinion is very weak in terms of both security and functionality and instead go for a product like TeamViewer (free for personal use) and you don't have to open any ports on your firewall to use it.

By the way, your attacker is coming from China....