watchgnupg is commonly invoked as
watchgnupg --force $(gpgconf --list-dirs socketdir)/S.log
watchgnupg understands these options:
$ watchgnupg --force --time-only $(gpgconf --list-dirs socketdir)/S.log
This waits for connections on the local socket (e.g. '/home/foo/.gnupg/S.log') and shows all log entries. To make this work the option log-file needs to be used with all modules which logs are to be shown. The suggested entry for the configuration files is:
log-file socket://
If the default socket as given above and returned by "echo $(gpgconf --list-dirs socketdir)/S.log" is not desired an arbitrary socket name can be specified, for example 'socket:///home/foo/bar/mysocket'. For debugging purposes it is also possible to do remote logging. Take care if you use this feature because the information is send in the clear over the network. Use this syntax in the conf files:
log-file tcp://192.168.1.1:4711
You may use any port and not just 4711 as shown above; only IP addresses are supported (v4 and v6) and no host names. You need to start watchgnupg with the tcp option. Note that under Windows the registry entry HKCU\Software\GNU\GnuPG:DefaultLogFile can be used to change the default log output from stderr to whatever is given by that entry. However the only useful entry is a TCP name for remote debugging.
The full documentation for this tool is maintained as a Texinfo manual. If GnuPG and the info program are properly installed at your site, the command
info gnupg
should give you access to the complete manual including a menu structure and an index.