This post has been edited because it is no longer correct. Read the replies for the updated information.
Duolingo never made the Tips for some of the smaller courses, like Klingon, available on the apps. You can access the Tips through a web browser, though. You don't even have to use a computer and there is a way to read them on your mobile device. If you login through your mobile browser, you can find the Tips for those languages that don't have them in the apps - like Klingon. Go to duolingo.com/learn.