The most obvious choice for skp to dwg conversion, i.e. SketchUp to AutoCAD conversion, would be of course to SketchUp as it has support export to 2D (DWG/DXF).
This can be achieved through the File ► Export ► 2D Graphics function found in the program. The result is a 2D vector file in .dwg format (version 13 or 14) that you can open in any CAD program. However, you may also prefer to export it as 3D DWG file, in which case you need to select File ► Export ► 3D Model function. More about this can be learnt from SketchUp Help Center.
If you do not have access to the commercial version of SketchUp, you will have to use some of the third party alternatives or dedicated 3D model / CAD converter that will allow you to convert skp to dwg.