As far as I understood , ( my spain is lousy ) Kalaita is right
There is NO difference between "woher kommst du?" and "wo kommst du her?
[ I think , in my opinion
"wo kommst du her?" "wo gehst du hin? "
is a little more used in general speaking
"woher kommst du? " "wohin gehst du? "
sound a little little little bit more formal , to me
...this could also be ment in a Philosophical sense ... ]
Its really hard to find a difference between those sentence
You can use both in any situation , you will never do wrong
You can use as you like without any probleme