ToÂ loop over each user name listing out their crontab. The crontabs are owned by the respective users so you won’t be able to see another user’s crontab w/o being them or root.
for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done
To loop over each user and know, which user does a crontab belong to insert – echo $ user
for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done