"Er is niets leuks te lezen in de wachtkamer van de dokter."
Translation:There is nothing fun to read in the doctor's waiting room.
After "iets" or "niets", adjectives get an extra -s. This is a remnant from the old cases system (the genitive, to be precise). You'll see it in all the sentences of this lesson.
I believe you should add this explanation to the tips and notes section (where by the way I found this typo: "It this skill" should be "In this skill").
The Tips & Notes are only available if you use Duolingo in your web browser, not in the apps. You can access them by selecting a skill and then clicking on the light bulb icon. Not every skill has such a section.