How to view command history of another user in Linux?

On Debian-based operating systems, doing tail /var/log/auth.log | grep username should give you a user's sudo history. I don't believe there is a way to get a unified command history of a user's normal + sudo commands.

On RHEL-based operating systems, you would need to check /var/log/secure instead of /var/log/auth.log.

Just tested the following, and it worked like a charm.

sudo vim /home/USER_YOU_WANT_TO_VIEW/.bash_history

If the user issued a command as in sudo somecommand, the command will appear in the system log.

If the user spawned a shell with eg, sudo -s, sudo su, sudo sh, etc, then the command may appear in the history of the root user, that is, in /root/.bash_history or similar.