To answer the OP, memorise whatever your company wants you to. If you are invited for a SIM ride, and they send you pitch and power settings, and speeds and flap speeds, then definitely memorise those.
Obviously Memory items, SOPs, and flows, need to be learned and committed to memory. Some air law, for example radar service definitions and responsibilities. Minimum take-off and landing separation from aircraft ahead. Wingspan for taxiways, (although this should really be placarded). Anything you might need to know while actually hand flying or taxiing and therefore can't dive into the books.
How long does the BCF last? Ditto crew and passenger Oxygen? Ditto Dragar smoke hood? Important to know - if you are using them you won't have time to look it up.
Traditionally some of the stuff you are expected to memorise is not to fly the actual plane but so that you can pass a type rating. It is very easy for a lazy examiner to go through the books and pull out figures, but sometimes those figures are meaningless. Cabin crew where I once worked had to know and answer correctly the frequency the ELT transmitted on. I mean, ??? Can you change the frequency? No. Do you ever have to alter the frequency? No. Can you select a different frequency? No. So why are you asking me what the frequency is? It is fixed so it is irrelevant.
Power output of a main generator in kW? Who cares? Meaningless unless you also know what the power consumption of all the various electrical systems are. You just need to know how many gennys are needed to supply the whole 'plane, and if you lose a main genny what services do you lose?
There are a few enlightened souls who are realistic. One TRE said to me " If I go and select an obscure or irrelevant fact from the books to ask you about, you could do the same to me, so I don't go there"
Engine limitations I believe should be shown on the instruments, e.g. is the max N1 104% or 103%?, I can't always remember, especially on mixed fleets. Give me a line on the dial, that moves for different flight phases, as Airbus do.