According to nginx docs, add line to your configuration file.
access_log /path/to/your/logs/nginx_access.log;
error_log /path/to/your/logs/nginx_error.log info;
To log with supervisor, you can add lines to your configuration file like this
[program:program]
command=/virtualenv/python /path/to/django/source/manage.py run_gunicorn --log-file /path/to/your/logs/gunicorn.log
stdout_logfile=/path/to/your/logs/supervisor.log
As you see, gunicorn log is specified in parameter log-file
Finally in django settings you can do the logging according to docs