The most recent version of this documentation can be found at https://docs.dyalog.com/20.0/.
The )EVENTS system command lists the Events that may be generated by the object associated with the current space.
For example:
⎕CS 'BB' ⎕WC 'BrowseBox' )EVENTS Close Create FileBoxCancel FileBoxOK
)EVENTS produces no output when executed in a pure (non-GUI) namespace, for example:
⎕CS 'X' ⎕NS '' )EVENTS