Some languages on Duolingo have audio and some don't. The commercial TTS that Duolingo uses does not include Klingon and the staff does not want to try to find voice actors who speak Klingon to go into the studio and record all the audio. However, the administration seems to be working on an alternative for us. We may have audio in the distant future.
There is a Skill a little bit into the course which teaches the names of the Klingon letters and has a description of the pronunciations in the Tips & Notes, however, that skill also lacks audio. If you want to check out some ideas for learning the pronunciation, check out the thread at: https://forum.duolingo.com/comment/26605745
If you want to read about the other known issues in this course, read the post at: https://forum.duolingo.com/comment/26778885
And finally, the only way I know of to complain to the administration about the lack of audio on this course is to file a bug report: https://support.duolingo.com/hc/en-us/articles/204728264-How-do-I-report-a-bug-
There seems to be a bug here. I had a listening question, and had two choices for "did you understand?".
The top one is correct, but I put the second which it accepted, which I think should be marked wrong? I've reported it to Duolingo so that they know as well and hopefully this will be fixed.