Hi @B_ryr,
journalctl is not a dnf subcommand, so you would want to run just sudo journalctl ....
The whatever here is the time until which you want to preserve your systemd logs. If you use:
sudo journalctl --vacuum-time=1s
then you would only preserve the logs for the last 1 second, so basically remove all logs.
Note that you can also run this command in TemplateVMs, not just dom0.