In ArchiCAD 12 the Ghost story has been replaced with the more versatile Trace Reference Functions. Look them up in the reference guide for a description of their use. Under the windows menu there is a Trace&Reference pallet that you can display or you can add it to your work environment as needed.
HTH
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K