Convert 3DXML to DWG

Since 3DXML format is more or less exclusively used in Dassault Systèmes software, your best and most likely only viable option for 3dxml to dwg conversion or export would be with CATIA or other software from Dassault Systèmes S.A.  Some commercial CAD/3D modeling converters might also be of help here perhaps, but freeware converters are extremely unlikely because the license for 3DXML format is not open source.