Due to issue a Linux service "Failed with result 'exit-code'." i wanted to enable OpenVPN server logging.

# locate {server,service}.conf|grep vpn
I have used found address to edit the file to enabled logging on server: nano /etc/openvpn/server/server.conf
by adding line "log /var/log/openvpn/log" making sure that path (file "log") exist (touch /var/log/openvpn/log).
Then restart the service: service named possibly discover using command "systemctl status --all 2>/dev/null|grep -i vpn|grep ●" (one having server in its name)
Then: cat /var/log/openvpn/log

Apparently it worked.