Is there a command that list all enabled Apache modules?
You need to enable the info module:
sudo a2enmod info.load sudo a2enmod info.conf sudo service apache2 restart
will provide a long list of modules, and configuration info.
To view from remote servers, you can change the 'Requires' option in /etc/apache2/mods-available/info.conf to allow remote servers to view info.
On more recent iterations of Debian and Ubuntu there is also the
a2query -m authz_host (enabled by maintainer script) ssl (enabled by site administrator) ...
Usage: /usr/sbin/a2query -q -m [MODULE] -s [SITE] -c [CONF] -a -v -M -d -h -q suppress any output. Useful for invocation from scripts -m [MODULE] checks whether the module MODULE is enabled, lists all enabled modules if no argument was given -s [SITE] checks whether the site SITE is enabled, lists all sites if no argument was given -c [CONF] checks whether the configuration CONF is enabled, lists all configurations if no argument was given -a returns the current Apache 2 module magic version -v returns the current Apache 2 version -M returns the enabled Apache 2 MPM -d returns the Apache 2 module directory -h display this help
The above answers are old and no longer work for my modern Fedora Server 31 / 32 and Apache 2.4.
Here's what does:
httpd -t -D DUMP_MODULES
But, there is a caveat that this will only work if you have an appropriately configured /etc/httpd/conf/httpd.conf, so if you're in the middle of editing to set LogLevel, it won't work if your edits are in-progress and not valid!