Where are the NetworkManager logs?

The answers are now obsolete (2017), the logs are now here

journalctl -u NetworkManager

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).

To reiterate Where are NetworkManager log files located for the network-manager package:

From the man pages:

man NetworkManager

  --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.