The Skilltree system of the Witcher 2 seems drastically simplified on first look. The complex skilltree of the first game is exchanged for starry sky and is broken down into four categories: Traninig, Swordsmanship, Signs and Alchemy. With every level up you get to spend so called talent points into your skills.
The maximum level you can reache in Witcher 2 is 35. With that said, keep in mind that you will not be able to max out every skill branch and once invested talent points cannot be removed. So carefully planning is the key to success here.