Question: I have learned that when someone wants to know where a person comes from, one must ask: 

> 
> Woher kommen Sie?
> 
> 
> 

A lot of people have asked me: 

> 
> **Wo kommst du her?**
> 
> 
> 

or 

> 
> Wo kommen Sie her?
> 
> 
> 

Indistinctly. So the question is what is the difference?

Answer: 
While the *meaning* of the two forms is rather similar, they derive from different starting points.

> 
> Woher kommen Sie?
> 
> 
> 

The question word *woher* is asking for a place you came from and the *from* is included in that question word. The rest is rather simple, the verb is *to come* just signifying a movement.

> 
> Wo kommen Sie her?
> 
> 
> 

Here, the question word *wo* asks about a static location and the directional aspect is included into the separable verb *herkommen* (*to come here*). So very literally translated it would be: *Where did you come here from?*, not *where are you from?* The literal translation gives a wrong picture though since the usage in English would be quite different.

You could even combine both forms (although that is rare) to generate:

> 
> Woher kommen Sie her?
> 
> 
> 

Usually, marking the directional aspect once is considered enough.

If I had to guess, I would term it a North-South dualism, but I’m not too sure on this.
"Woher kommen Sie?" is a more formal and slightly outdated version of "Wo kommen Sie her?". Both mean "Where are you from?" (or literally, "Where do you come from", as in "what place/event were you at before you arrived here" but it is less often used to mean that).

"Woher kommen Sie?" is not used in spoken language very often, as far as I'm aware. (I'm German, from the Cologne area). It sounds stilted.