Startup slic in a mode where Geant4 will be initialized. For instance, you can start in interactive mode.
slic -n
Or you can load a geometry file.
slic -g mygeom.lcdd
The splash screen printed by the G4RunManager shows the Geant4 version, similar to this.
*************************************************************
Geant4 version Name: geant4-08-02 (15-December-2006)
Copyright : Geant4 Collaboration
Reference : NIM A 506 (2003), 250-303
WWW : http://cern.ch/geant4
*************************************************************