During the build, the output is displayed in the Application Build output pane. This is a normal editor text box which you can search and edit in the usual way.
If there is an error during the build, a backtrace is generated and the subprocess image exits.
To view the error message choose
Works > Build > Display Error
or click the 
toolbar button.
To view the error message and the backtrace in an Editor tool choose
Works > Build > Display Backtrace
or click the 
toolbar button. Most errors can be resolved after checking the backtrace.
To clear the Application Build output pane choose
Works > Build > Clear Output
or click the 
toolbar button.
You can set the tool to do this automatically - for the details see Configuring the Application Builder.
LispWorks IDE User Guide (Windows version) - 13 Sep 2017