Quick hint: Use visudo
And: sudoers doesn't live in /etc as in many Linux; it is in /usr/local/etc
Other than that sudo on Linux and FreeBSD are essentially the same from a config file perspective.
Originally Posted by SSSlippy
Yes indeed - the FreeBSD "Handbook" should always be a first stop for FreeBSD users and administrators.
isn't part of the FreeBSD operating system. It is an add on package, and thus it's documentation is to be found elsewhere.
On the OP's system, run:
pkg_info | grep sudo
With the version returned from that:
pkg_info -do sudo-18.104.22.168
... and that will tell you more about the package; where in the ports tree it lives (security/sudo) and often a website you can visit.
I suggest also installing from ports pkg_search:
Which will allow for searches like:
$ pkg_search -r sudo