To determine which is the nearest Zscaler DCs for the specific IP or machine. Here are some commands that you can use to achieve that:
You can run the below command in your command prompt to see the nearest DCs for specific IP.
Replace the IP with your public source IP:
curl https://pac.zscaler.net/getGatewayEndpoints?srcip=115.112.60.134
Or, you can run the below command directly to get the 3 nearest DCs for the machine on which it is running:
http://pac.zscaler.net/getGatewayEndpoints
Once you gotten the best 3 DCs, can copy the IPs from the output and match it with the config page.