"Torg, did you understand Mara?"
Translation:torgh, mara Dayaj'a'?
To add to what had been explained, I want to make sure you notice that in the first sentence Mara's name is being called and is not part of the question being asked. In English, when you call someone's name, you can do it before the question or after the question. The same is true in Klingon. So if the English sentences calls her name after the question, then so would the Klingon translation.
In the second sentence Torg's name is being called and Mara's name is actually being used as part of the question. Now both English and Klingon have specific places where Mara's name must go (and those places are different in the two languages). However Torg's name could go either before or after in either language, so should match in both versions.
"Did you understand?" has no object. The sentence doesn't say anything about what or who is understood, it just asks about understanding in general.
"Did you understand Mara?" has an object: Mara. She is the one who is being understood.
Klingon verb prefixes show not only the subject but also the object.
So even though the subject is the same in both cases (so in English both sentences use "you"), the object is different -- no object in one case, third-person singular object in the other case.
So one sentence uses bI- (with capital i, not bl- with small L) for "subject = you, no object"; the other uses Da- for "subject = you, object = him/her/it/them". (In this case, "object = her", i.e. Mara.)