Hi educell, it looks like a problem in your Linux settings. The package does not even begin to install. I don’t know if ppa can be used in a chromebook. In this particular case, according to your error traceback is clear your Linux installation is not complete to use add-apt-repository because it complains of a missing package, gpg. This thread https://www.reddit.com/r/Crostini/comments/91a4i4/trying_to_add_repo/ seems to provide a solution.
If that solution fails, you can download the package and install it manually, without apt, doing sudo dpkg -i kolibri_0.11.0-0ubuntu1_all.deb
Hope it helps