This is an example sentence from 大辞林's definition of 定める.
I think this means something like "punish according to the law". But couldn't you just say 法律により処罰する? What does 定めるところ add? What does ところ refer to?
Is 法律 the subject of 定める? Maybe not, because in another example sentence, 規則 is marked as the object:「規則を―・める」