Each "whether" demands "or not" to follow. However, in case of indirect questions you don't need "or not" :Originally Posted by alan
ex. "I asked her whether she knew how to get to the new movie theater".
Mind you, you can also use "if" in that example and it will still be correct .
If you want to express a set of possibilities or alternatives, you will want to use "whether".
I am going to the beach whether it rains or not.
I am telling whether you like it or not.
The President was wondering whether to proceed with the speech or to leave it for later.
Also, "whether" can be followed by another "whether" :
Whether we win or whether we lose, we are going to stay the course of the whole season.
hope it helps