I’m not sure _____ to class even if the Corona Virus State of Emergency ends. I prefer online study; it’s smarter, safer, easier and saves me money & time. (Both choices are grammatically correct, but one is useless and means something very different from the other.)
In my opinion there are two reasons to offer here.
The answer is about going, because:
① when we are or are not sure regarding something, we use ‘about’ as the preposition to connect the subject to the object we are discussing.
I’m sure about this information. Trust me.
I’m not sure about this. We’d better check it on Wikipedia.
John is sure about the spelling; he looked it up in the dictionary.
Similarly, we use sure about with the ‘ing’ form of verbs as nouns (called gerunds).
I’m sure about depending on this information. Trust me.
I’m not sure about trusting this information; we’d better check it on Wikipedia.
John is not sure about spelling this word; he couldn’t find a dictionary to use.
And the answer is “about going“ because ② ‘not sure to’ means “not certain” from the point of view of others, just as “sure to” means “certain” from the point of view of other people, not from the point of view of the speaker. Look:
It’s sure to rain.
Nature is not sure about rain coming–or happening. The situation is certain, or we are certain… that rain will come.
Bob is sure to be here on time. He is never late.
We are sure about it; Bob is not thinking about it.
We use about (meaning “regarding” or “concerning”, whereas sure to means “supposed to” or “expected to.”
After I’m not sure, we need a noun in this sentence, and about is the right preposition to precede a noun. We use about with true nouns and proper nouns all the time. Look:
I like books about traveling in space. Or... I like books to travel in space.
‘Traveling in space’ is not a verb, and it doesn’t look like a verb, either, but if we replace it with t0 travel in space, it looks like a verb and sounds like a verb and the whole meaning of the sentence changes to “I like books as a method of traveling in space.“ It’s like the speaker flies on books and not in spaceships!
So, About is used to mean regarding, “concerning” and “in the case of” and that is what we need after “I’m not sure.“