You would 99% do a medical knowledge exam in order to get the Approbation. I do not know further details. You can find the further details about the content of the exams and the exact required documents for application in the websites of the medical license authorities in the mentioned authorities.
1) Baden Württemberg: http://www.rp.baden-wuerttemberg.de/servlet/PB/menu/1071540/
If you applied for Approbation in any of the above authorities, then please post your experience as a comment.
If you know of other authorities, then please also write a comment.
Read further details about the applying for the Approbation here in Germany (highly recommended):