How can I log ftp debug information?
I added in /etc/syslog.conf:
daemon.debug /var/adm/syslog/syslog.log
and then I stopped and started syslogd but it does not log anything...
From memory, you'll need to look at how the ftpd service is set up. It requires the '-v' (lower-case 'v') operator to be issued.
It's executed by inetd so you should see a reference to ftp in the inetd.conf file (HP-UX).
Check out: man ftpd & man inetd
Hope I got that right and it is of some help to you. 
Cheers,
Cameron