List all files in a homebrew package
Just add -v or --verbose, for example:
$ brew ls --verbose exim
If the package in question is a cask install (e.g. mactex) then you'll need to include the --cask arg to the list/ls command e.g.
brew ls --cask exim
Note: With casks if you don't include the --cask arg then it often reports an error. And with the --cask arg it may only list the installer dmg as it doesn't seem to track the resulting installed files.