Where can I find the configuration files for Kdenlive?
The config file for kdenlive is located in
~/.kde/share/config/kdenliverc
And / or:
~/.config/kdenliverc
Additionally, there's also a directory
~/.kde/share/apps/kdenlive/
And
~/kdenlive
Which contains additional configuration data, including export profiles, video file information and so on, so you should back that up too.
To see the .kde directory, you'll need to enable "Show hidden files" in your file manager. In Nautilus (The default Ubuntu / Unity file manager), you can do so with ctrl + h