As you said yourself, it’s a beginner problem. When you know the words, it’s obvious 99.9% of the time. In this case, かもしれない is a word on its own. なの is often required grammatically, depending on the structure.
Oh, I see, it’s かも知れない on jisho, and it means “may, possibly”… Wanikani will never teach me this word, so how do I know it? Well, let me rephrase that: when WK doesn’t teach you all the words, how do you recognize the words you don’t know, when they are not clearly distinguishable in a all-together sentence??.. is there any trick or something??
aaah, I understand!!.. なの is “expectation and explanation” in Tae Kim’s guide!!.. the only difference is that in Tae Kim’s example sentences it’s always at the end, while here it’s in the middle, so I didn’t recognize this particle as such, and I stupidly thought of なのか being 七日
eeh, I really need a better resource where to study the grammar!!.. I will go for The Dictionary of Basic Japanese Grammar, seems so serious and well made…