"I'm reading that book now."
Translation:DaH paqvetlh vIlaDtaH.
Duolingo takes a simplistic approach to the continuous suffixes: if it uses a progressive tense in English, it uses a continuous suffix in Klingon, as if these things had a one-to-one correspondence.
This isn't really correct, though. One must distinguish when English uses the progressive tense to actually mean something continuous, or whether it's just a conventional style. For instance, there's no rule that says we couldn't say I read that book now, but it sounds stilted, because we automatically use the present progressive whether the action is continuous or not.
DaH paqvetlh vIlaDtaH means that now you are in the ongoing activity of reading that book. DaH paqvetlh vIlaD means that that book is the book you identify as the one currently at the top of your reading list (or whatever). Both might be true, but you can only express one at a time. English uses one sentence for both meanings.
Unfortunately, Duolingo doesn't support these more accurate meanings of the continuous suffix, so you'll have to artificially use -taH or -lI' whenever the English sentence uses a progressive tense.
Thanks for the help with that. I was really referring to the fact that Duolingo was quizzing me on something that hadn't even been taught yet, making it impossible for me to give a correct answer since it was a question where I had to type in the correct answer. (If I had just had to choose from a limited set of words, I may have been able to do that, although I would have been confused, but it's impossible to type in a word you haven't been taught.)