Ubiquiti kit is great, and Unifi is by far the best value for money WiFi kit out there. However once you get beneath the beautifully crafted UI and you’ll soon struggle to find CLI info and configuration help.
Yow to find your VPN log Unifi
SSH into your USG, using your site specified SSH credentials, or if you have never set any, then ubnt/ubnt.
Then simply type:
show vpn log
or:
cat /var/log/charon.log | tail -n 100
Simple.