Logging is done using journalctl
.
See for example https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs
See http://pm2.keymetrics.io/docs/usage/log-management/
pm2 logs
/root/.pm2/logs/pm2.log
/var/local/logs/webic-out.log
/var/local/logs/webic-err.log