Generally when you log into another user account, the bash history will be saved in a file called .bash_history located in the home directory of that user.
Use: Su vim ~/.bash_history. History does not save the command if it has a space in front of it. This is dependent on the HISTCONTROL variable. By default (for root) it's ignoredups:ignorespace.
You can run the history command to see the current users history.
They are written into .bash_history on exit: When an interactive shell exits, the last $HISTSIZE lines are copied from the history list to the file named by $HISTFILE.