The first place where PATH is set is
/etc/login.defs. There's a setting for root and a setting for everyone else.
Another place where you can define environment variables is
/etc/environment. These settings will apply to everyone (you can't write arbitrary shell code there).
A third place where you can define environment variables is
/etc/profile. There you can write arbitrary shell code. If you want a user-specific setting, there is the corresponding per-user file
~www-data/.profile. But this will only apply to console interactive logins; in particular it won't apply to cron jobs unless they explicitly source
If you only need that
PATH setting in a user crontab, you can write it at the beginning of the crontab. Note that you need the full list (
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/zend/bin), you can't use a variable substitution (
PATH=$PATH:/usr/local/zend/bin won't work there).