The logs can be found at the following file paths.

Master: <Master installation directory>\MasterLog (e.g., c:\Master\MasterLog)
Agent: C:\Users\<Username>\AppData\Local\PIX\PIX Agent

Studio: C:\Users\<Username>\AppData\Local\PIX\PIX Studio
The studio log files can also be opened by pressing Ctrl+L or by clicking the "Open log file" button in the upper panel:

Increasing the logging level of the Master

The level of the Master's logs is adjusted in nlog.config.
Main line: <logger name="*" minlevel="Error" writeTo="ownFile-web" />
You can adjust the value in the minlevel attribute to extend the logging.
Possible options: Error, Warn, Info, Debug, Trace.