you will have to chase down Geppetto’s kidnappers in Lies of P. This will take you to Relic of Trismegistus where you will have to face off against the Eldest of the Black Rabbit Brotherhood ...

The Portrait can be found in Chapter 5 of Lies of P, in Malum District. In Malum District Town Hall, you need to defeat the Eldest of the Black Rabbit Brotherhood as the main boss of the area ...