"Mara does not understand Torg."
Translation:torgh yajbe' mara.
Yes, that is correct. There is no comma anywhere in either the Klingon or the English sentence. If there were a comma after yajbe' it would be separating Mara's name from the sentence, indicating we were calling her name and talking about someone else. Without the comma it indicates, instead that we are talking about her and gives no indication who we are talking to.
Yes. You are correct, but there's an interesting thing that happens when the subject and the object are third person. We have something that we call a "null prefix", in other words, the absence of a prefix. It gives us information just like any prefix that you can see and hear even though this is actually the absence of a prefix. So when you see a verb in a sentence without a prefix, that also contains information about the subject and object. Because there is no prefix on the verb, we know that the subject does not include either you or I and that the object also does not include either you or I. If we had no context an no additional nouns in the sentence, a complete sentence like yaj. would be pretty confusing and unclear. Does it mean "She understands," "It understands," "They understand," "He understands it" She understands them," etc. If we present a sentence like that, we have to accept all those variations as possible translations. Fortunately, in this sentence we are told who that third person subject is and who that third person object is, so it's easy to translate it.
Why isn't it "mara yajbe' torgh"?
Because that would mean "Torg doesn't understand Mara".
Klingon sentences have OVS word order: object – verb – subject.
In this sentence, "Mara does not understand Torg", the subject is Mara -- she is the one who (not) doing the understanding. And the object is Torg -- he is the one who is (not) being understood.
So in Klingon, the subject mara has to be after the verb yajbe' and the object torgh has to be before the verb.
So "Mara does not understand Torg" is torgh yajbe' mara.