You've unnecessarily changed the order of the sentence components -- the Klingon has the "..., mara?" at the end and so the best English translation also has "..., Mara?" at the end.
Some learners think of Klingon as "backwards English", so one reason that we insist on keeping the same order with such names, or with pairs of words joined by "and" (e.g. torgh mara je = "Torg and Mara", not "Mara and Torg"), is so that learners don't simply "read from the end to the beginning", translating as they go -- but understand that it's just the object - verb - subject structure that is unlike the usual order in English, not that everything is "simply back to front".
"Mara, do you speak English" and "Do you speak English, Mara" are different sentences. They basically mean the same thing, but occasionally there's a reason why you would want the two parts to be in a particular order. If you put the name of the person you're speaking to last in the Klingon, then you should put the name of the person you're speaking to last in the English.
It is part of the trigraph tlh. The consonant tlh is actually one sound and considered one character in Klingon even though we write it with three letters in our Roman transcription system. It is also written as an uncapitalized letter as part of the digraphs ch and gh. Whenever you see it uncapitalized it should be one of those three consonants and whenever you see it capitalized, it should be the consonant H.
That will be explained in the Tips & Notes for the Sounds Skill, where the letters of Klingon are introduced and described. 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 Tips button.
If you click on the Tips button 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 any Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
Is "-'a'" verb suffix just indicative of the interrogative?
The verb suffix -'a' makes yes–no questions.
So it's used in questions such as "Do you speak Klingon?" or "Have you eaten yet?", but not in WH questions that have a question word such as "who, how, when, why, how many, ..." in them.