You want to list all the packages which can be configured with debconf
A very easy way to do this is to list all the directory /var/lib/dpkg/info and filter out the ones with config at the end.
ls -l /var/lib/dpkg/info/*.config
These packages can be configured with debconf.
An easier way is to use the command "configure-debian". You will get a selection of programms which can be configured and is interactive. You can also use this command to reconfigure packages.
About the Author
Wim Peeters is electronics engineer with an additional master in IT and over 30 years of experience including time spent in support, development, consulting, training and database administration. Wim has worked with SQL Server since version 6.5. He has developed in C/C++, Java and C# on Windows and Linux in different European countries and different European languages. He writes knowledge base articles to solve IT problems and publishes them on the Lubby Knowledge Platform where he is one of the most important contributors and the main developer.