Translation:The soldier asks if I can cover him while he is running.
I translated as "The soldier asks whether I can cover him while he is running". Why is it wrong? Do I have a wrong understanding of how "whether" works in English?
You are correct, but sometimes the translator does not recognize that "if" and "whether" can be equivalent in English. You may run across the same problem with "hvis"
this might be completely wrong but as a dane myself I would understand questions like this as a bit of a command instead of a genuine question. I mean your translation is correct by maybe Duolingo knows that danish isn't a polite language...
Your use of "whether" in this case is correct. I have noticed that sometimes translations that are really correct may be labeled incorrect. There are some glitches.