Is the "or not" in "whether or not" optional? [duplicate]

Whether is used to form indirect polar (yes/no) questions. A polar question refers to two conditions, but they are logically related and so one condition can be inferred from the other.

From a functional standpoint, then, [or not] is superfluous. Not surprisingly, most indirect questions formed with whether can have [or not] omitted.

A separate issue to be raised, if you choose to keep [or not], is where to place it. You can choose either:

...whether [or not] the frail patient has an infection.
...whether the frail patient has an infection [or not].

The best guideline is that when the proposition under question is "heavy" (many words), use whether or not..., and when it is "light", use whether...or not.