Do the words or not always follow the conjunction whether? Here's the rule: When the clause beginning with whether is acting as a sentence adverb modifying the main clause, it must express two possibilities: Whether I go or stay home, you can attend.
If only one possibility is stated, include or not as the second possibility: Whether I go or not, you can attend; Whether or not I go, you can attend. (Tip: In this case, whether or not is equivalent to regardless of whether.)
In all other cases, or not is either incorrect or unnecessary and can be omitted. Now that you know the rule, you can decide when to omit the words or not in the sentences below.