A previous poster on the regular forums ( http://ubuntuforums.org/showthread.php?t=843991 ) said
/var/log/daemon.log, but I don't seem to have such a file. Do I need to enable logging?
You can find the Network Manager logs in
/var/log/syslog, which acts as a catch-all for log messages (unless you have changed rsyslog's default configuration).
The answers are now obsolete (2017), the logs are now here
journalctl -u NetworkManager
To reiterate Where are NetworkManager log files located for the network-manager package:
From the man pages:
--log-domains=<domain1>,<domain2>, ... Sets which operations are logged to the log destination (usually syslog). By default, most domains are logging-enabled. See NetworkManager.conf(5) for more information on log levels and domains.
If you're using Ubuntu 16.04 or later,
should show all the NetworkManager logs.