Student or Learner
The law that don't.... or The law the doesn't....
There is a certain rule?
I, we do.../...don't (= do not)
he, she, it does.../...doesn't (=does not)
they do.../...don't (=do not)
The law (it) : hence, "The law doesn't..."
I'm not a teacher but ..
I think ( that doesn't ) is the right choice ..
because when you are talking about a fact or a habit and what you are talking about is singular and it includes (she , he , it )you should use ( doesn't )
Ex: He doesn't know about the accident
and if you are talking about a plural (includes the word "you") you should use ( don't)
They don't know about the accident .
You don't know about the accident.
Of course the teachers know better ^_^