Lync Client Log Files

To turn on Logging
In the Communicator Title bar, click the Menu button, point to Tools, and then click Options.
Click the General tab, and then under Options, select the Logging options that you want to enable.

To locate the Communicator log file
In Windows Explorer, navigate to the <user profile>\Tracing folder. If you have enabled the Turn on Logging in Communicator option, you will see a communicator-uccp-log.uccplog file in the folder. If you are already signed in, you will need to sign out and then sign back in before the log file is created.

Also lync 2011 for mac log files are located: 

/Users/username/Library/Logs