One google later:
Hawaiian has a full spread of proximal-medial-distal demonstratives, while English no longer marks for medial vs distal (although it used to, with "yonder" contrasting with "that). "Kēnā" is the medial demonstrative, while "kēlā" is the distal one.
Thanks! Now that you mentioned it, I remembered that there is a Kēlā & kēnā section in the Tips and notes for the Determiners skill:
I guess without any context, either one should be accepted, although this might have been a word bank exercise (don't remember exactly) where only "kēnā" was provided as a valid translation.
If you speak any Italian, you can use the word "là" as a mnemonic for "kēlā" (at least that's what works for me)
You should have buttons with the vowels with the macrons over them. If you are on a mobile device, it may not have them. May I suggest that if you are indeed on a mobile device you update the Duolingo app and see if that makes them appear.