The 
Reverse Engineering Workbench is intended to give you specific tools to convert shapes, solids, and meshes into parametric FreeCAD features. It is still in development.
At the moment there is no functionality present in this workbench. It is used as a sandbox by the programmers.
The Reverse Engineering tools are all located in the Reverse Engineering menu and the Reverse Engineering toolbar that appear when you load the Reverse Engineering workbench from the workbench dropdown menu.
Approximate a B-spline surface:
Link to appropriate threads discussing this workbench
documentation index > [Reverse Engineering](Category_Reverse Engineering.md) > Workbenches > Reverse Engineering Workbench