As far as I know, every kanji question is always a real word (or maybe sometimes a suffix/prefix). There is only ever one valid reading for the word listed in the answer list. So there is never a situation where you are given two answers that are alternative possible readings which you have to choose between; it's always one correct reading and three incorrect readings for the word shown in the question. So the correct answer might be onyomi, or kunyomi, or both... or NEITHER!!
Example: The lesson 5 kanji question "日曜日" isn't just a random string of kanji where you have to find onyomi or kunyomi for each of its kanji. As you probably already know, 日曜日 is an actual Japanese word and there is only one answer given that is correct for pronouncing this word (no matter whether it is kunyomi or onyomi). In fact, for this question it's both!
日曜日 = にちようび "nichiyoubi", meaning "Sunday".
日 = にち "nichi" (ON reading)
曜 = よう "you" (ON reading)
日 = び "bi" (KUN reading)
November 16, 2015 at 1:10am