/etc/X11/Xsession.d/70xdg-kubuntu-dir is in kubuntu-settings-desktop 1:18.04ubuntu11.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # Added a path to put Kubuntu Settings
XDG_CONFIG_DIRS="$XDG_CONFIG_DIRS:/usr/share/kubuntu-default-settings/kf5-settings"
|