During development, the Studio log file and UI designer log file contain messages about development activities, including any errors. When you run a process for testing, messages are written to the Engine log file.
From the Bonita BPM Studio Help menu you can access the Studio log file
and the Engine log file. The UI designer log file is available in <bonita.home>/tomcat/logs/ui-designer.log, but it is not accessible from the Studio Help menu.
See the Logging overview for details of how logging is implemented in Bonita BPM and how to add logging to Groovy scripts or Java code that you add to a process