Shareware Duke Nukem 3D data has been installed to: 
  ${PREFIX}/share/duke3d/

You may also copy your registered version data files (or any other
Duke Nukem 3D retail copies, such as the Atomic Edition) to a local
directory such as ~/duke3d, and run eduke32 from within that directory:

  % cd ~/duke3d && eduke32

This will load your registered version data rather than the installed
shareware.