Where log information can be found for debugging
There are log files on the client, which are most useful for figuring out why a client is having problems making a connection to a server, and figuring out which routes and instructions it is receiving. And there is the Log Reports section in the Admin UI which is generally used to figure out when a user connected, for how long, when people logged onto the web interface, how much data they've used, and if there were any simple type of errors when authenticating and connecting.
On the server, there are log files that contain technical information, and this technical information can also instead be sent to syslog locally.
Locating the client log files
Locating the server log files
Setting up log rotation for /var/log/openvpnas.log.*
Logging to syslog instead of the standard log file
Redirecting to an external syslog server
Implementing a listed debug flag
Log Database Guide