Is this sentence correct?
He is not sure whether or not he looked at his side mirror or whether or not he shoulder-checked before he turned to New York Street
I see nothing wrong with:
He's not sure if he looked in his wing mirror (side mirror)........
In order to use whether, there should be a choice between two things he might have looked in:
He's not sure whether he looked in his side mirror or his rearview mirror before he....
However, I'm not quite clear if he is unsure about one thing or two. Does he think he definitely did one of those things, but he can't remember which one? Or is he not sure that he did either of them?