This document seeks to serve as a central repository for information regarding debugging, i.e. to see what's going on under the hood of various programs.
There's a log file at $HOME/.config/lxqt/debug.log that will populate with information using QLoggingCategory.
There's a few ways to turn this logging on, but the easiest way is to add the following before exec lxqt-session in /usr/bin/startlxqt:
which turns off all debugging except for those messages with the lxqt-session category.
At time of writing, other LXQt applications use qDebug, which just prints to stderr. Running with 2>/path/to/some/file will get that output. Since startlxqt runs all the applications in /etc/xdg/autostart, any of these files can be edited so that their Exec key includes this addition.
See also /var/log/installer/debug
To start Calamares in debug mode sudo calamares -d. Debug mode will give information regarding the modules that are loaded and the associated settings.