Should I use "whether or not" or just "whether" in following sentence? Which one is correct?
I kept contemplating whether or not to sell my stock position.
I kept contemplating whether to sell my stock position.
We often use whether-clauses to represent closed questions. This means they often represent questions which have the answer yes or no.
So there are two possible answers to the question Should I sell my stock position?: YES and NO.
In English, when a whether-clauses represents a closed question, we do not need to represent the no option in the clause. (In many other languages you do need to represent the no option).
However, although we don't represent the no option, we can if we want to. This does not change the meaning of the sentence at all. There are two ways we can do this:
In the first example, we see the words or not appearing after the word whether. In the second example, these words appear at the end of the clause instead. Both of these examples are grammatical.
In English, sentences (1), (2) and (3) are all grammatical and all mean the same thing. For this reason both of the Original Poster's examples are grammatical and also have the same meaning.
We can also use whether-clauses to make special conditionals called exhaustive conditionals. When we use whether-clauses in conditionals, they MUST include all the possible outcomes of the situation—otherwise they are ungrammatical. Usually this means that they must contain the words or not: