"Did you understand, Mara?"
Make sure to read the Tips & Notes for each of the skills before you start them. Many of these important grammatical details are explained there. If you single click on the skill it should show you a small light bulb and if you click on the light bulb, you will get those Tips & Notes explaining what you need to know for most of the sentence in that skill.
Klingon doesn't mark tense, so bIyaj'a'? could be either past, present or future: "Did you understand? Do you understand? Will you understand?"
Also, note that the prefix bI- contains a capital i, not a lowercase L -- it's not bl-. (Note the tiny curl at the bottom of an L l versus the capital i I which has no curl at the bottom.)
While the prefix bI- shows that the subject is "you (one person)" and that there is no object, the prefix Da- shows that the subject is "you (one person)" and there is a third-person object "him, her, it, them".
So Dayaj'a'? could be something like "Did you understand him? Do you understand it? Will you understand them?".
To clarify the object, you could use a pronoun (e.g. chaH Dayaj'a'? "Did/Do/Will you understand them?" with chaH "them") and to clarify the time you could use a time reference (e.g. wa'Hu' Dayaj'a'? "Did you understand him/her/it/them yesterday?" with wa'Hu' "yesterday").