"Does Mara understand, Torg?"
Translation:yaj'a' mara, torgh?
The order is indeed OVS. For this sentence: mara is the one doing the understanding (the subject), and as the thing that she understands is not specified, there is no object. Torg is the addressee which is not a subject or an object of the verb. The one addressed might be found either in front of the sentence, or after it, but the course requires that you put the addressee in the same place as the original sentence.
the -'a' makes a statement into a yes/no question, so it would be like adding "Does (s)he..." or "Is (s)he". This is contrasted with questions which use question words like "what" or "where", in that case do not use -'a'. One might say that as question marks are optional and not "native" to Klingon, that one or the other method is needed to indicate a question (but never both at the same time). So for example, nuq 'oH ponglIj'e'="What is your name?" (no -'a'). torgh 'oH'a' ponglIj'e'="Is Torg your name?" (no question word, -'a' used). Or, nuqDaq 'oHtaH tengchaH'e'="Where is the space station?" (question word, no -'a'). naDev 'oHtaH'a' tengchaH'e'="Is the space station here?". If the -'a' were left off, naDev 'oHtaH tengchaH'e' would mean "The space station is here" (not a question). Hope that helps.