Exciting day today as Oracle Database 12c is released. You can find lots of information on the release on OTN here. With this release comes another milestone on Oracle's Data Integration roadmap - OWB is no longer shipped with the database. You will notice that the OWB documentation is no longer included with the Oracle Database documentation, you can compare and contrast the 11.2 and 12.1 documentation below.
OWB 11gR2 is still supported with Oracle Database 12c, you will need 126.96.36.199 plus at least CP2 which has been certified with Oracle Database 12c. The 188.8.131.52 release will wrapper this into one install.