sporting, don't waste your time reading a whole book, it won't help you. as far as financial knowledge is concerned - you need to have market-awareness, e.g.:
current interest rates of ECB, BoE, the fed
SPX, FTSE, NASDAQ, etc. have a quick look at them on the day you're going in.. and know how they've behaved over the last year.
wots a option/future? know how options are priced if u want to spend hours reading. definately know the greeks and wot they mean..
to get picked u don't need to be some financial guru.. in fact they hardly recruit people like that, maths is much more important to them - something i never understand..
generally, if you want to spend hours reading, think about how interest rates might affect equities or exchange rates, or other market factors.. e.g. if the fed hikes the rates to 6% wot would happen in the futures market? these r more advanced questions but if you'r reading a whole book u might aswell learn these.
definately know straddles, they constantly use it.. even if they don't directly ask u about it, u might use it when descibing how u might take a position on a trading scenario.. i'm surprised u'r not given a simualtion, typically you're given a trading simulation with other candidates..
hope that helps.