Let's for example test the package
apt to get the config file(s).
It can be tricky to understand what
.conffiles you should check to see the info so I suggest using
grep to find the clue.
locate *.conffiles | grep apt
cat any of these in particular if you are interested according to Marcin's Kaminski answer.
Another trick is to read the manual, for instance
man apt will lead you to SEE ALSO section from where you can call
man apt.conf where you will see the location of the config file for
apt in this case:
However, config file
/etc/apt/apt.conf may not even exist. Be aware of that when searching for the config files.
In Linux config files should be inside the
/etc/ directory. You may use
dpkg-query -L your_package | grep etc to list all package files and directories inside the