"Mara, do you understand?"
Correct. The -'a' verb suffix turns a sentence into a yes/no question - much like the word "do" in the English version.
"Mara, you understand." mara, bIyaj.
"Mara, do you understand?" mara, bIyaj'a'?
N.B.: This is only to form a yes/no question. The -'a' suffix is NOT used with who, what, when, where, why, and how questions (which will be covered later). Do not allow yourself to think of the -'a' suffix like a question mark.
A fairly good explanation is given in the Tips & Notes. It’s a lot of information and some details are bound to slip through. But since Duolingo has hidden the Tips & Notes I want to make sure you know about them and where to find them. If you have not been reading the Tips & Notes, I would like to ask that you review those so we don’t have to continuously repeat the information that we have explained there.
If you are doing the course on iOS or Android, you cannot currently access the Tips & Notes through the app. To access the Tips & Notes, you will have to access the course using a web browser at https://www.duolingo.com/. You can still do it on your mobile device, but you will have to use the web browser instead of the app (or you can do it from a computer). When you click on a Skill, it will expand to reveal a Start button and a light bulb (and a key, which is not pictured below, but is how you can test out of a Skill).
If you click on the light bulb it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes for the previous and current Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
Neither one is an actual word in Klingon. the proper word should be spelled with a capital i. If you look carefully, you can see the small curl at the bottom of lower case L which is missing from the capital i. So the word should be bIyaj'a'.
There are no consonant clusters in Klingon, so blyaj'a' is impossible. The i should always be capitalized in Klingon, so there is also no such word as biyaj'a'. Unfortunately the Duolingo software sometimes changes the capitalization. There is also no upper case B, but you might even see Biyaj'a'. This is a problem with the software and I hope that as you continue the course you will learn the correct pronunciation, but also learn to understand when Duolingo does it wrong and how to ignore it.