In my my_application/settings.py file, for example, I have a couple of print statements, thus:

print( 'running settings.py: ALLOWED_HOSTS: ' )
print( '\n'.join( ALLOWED_HOSTS ) )

... where does this output actually go on a remote server running nginx and Gunicorn?

NB I am aware this may be an egregious security breach to print ALLOWED_HOSTS anywhere, for all I know. This is merely an example: I am at the learning/experimentation stage.

Edit after AKX's answer
I found no way of getting stdout to be directed to journalctl, even with the -R switch.

... after many experiments and frustrations and baffling 502 errors, I finally found a way: my systemd config file now looks like this:

[Unit]
Description=Gunicorn server for mysite.xyz

[Service]
Restart=on-failure
User=mike
WorkingDirectory=/home/mike/sites/mysite.xyz
EnvironmentFile=/home/mike/sites/mysite.xyz/.env

ExecStart=/home/mike/sites/mysite.xyz/virtualenv/bin/gunicorn \
    --bind unix:/tmp/mysite.xyz.socket \
    -R \
    --capture-output \
    --error-logfile /home/mike/gunicorn-error.log \
    superlists.wsgi:application

[Install]
WantedBy=multi-user.target

... indeed, I find that it is not sufficient to include the -R switch: you also seem to have to include the --capture-output switch and the --error-logfile switch (NB I am not clear whether there is a default destination for error output if you don't set that switch).

With the above config file, stdout from settings.py goes to the file ~/gunicorn-error.log. Hurrah.