@Dario > There are no drivers needed for the DDJ-RB with Mac, but you can check that you're using the latest firmware here.
Disconnect the DDJ-RB, go to Applications > Utilities > Audio MIDI Setup, if you don't see your MIDI Studio window, open it from the Window > MIDI Studio menu item. Find the DDJ-RB item (if it exists; you may have to scroll to the right), and select it, then click Remove Device. Reboot your computer, launch rekordbox, reconnect the DDJ-RB.