Hello,
Ping is a router network administration software utility and as a feature, it is available all the time. It does not matter if you do have OpenVPN configured or not you can use this command.
Please navigate Services > CLI and enter the username (root) and password (your router WebUI password). Then simply write ping X.X.X.X.
X.X.X.X is an IP that you want to ping.
Regards.