"Platinum & Palladium Printing" by Dick Arentz. The bible..on this process. Carl Weese/Dick Sullivan "The new platinum print" Excellent book on a more practical approach less sensitometry and more "hands on" how to book.
"Comming into Focus" edited by John Barnier. Many, many alt processes including pt/pd.
Of all the books I bought these 3 are the best IMO.