There's a good Piper-published sales-type book around which contains all the systems info but (unfortunately) some highly optimistic performance info. Dunno who sells it.
If you only need generic info, the systems are effectively the same as Seneca 1 (and several other Pipers) but this is obviously no good for answering a CAA examiner.
Typical systems questions might be: why did the designer choose to use flaps that create a slot when they're down, what type of ailerons (and why), what's the advantage of a stabilator, how is the gear held up, how does the emergency drop work, how does the auto drop mechanism work (and at what speed), what does the prop do without an oil supply, where do you find the list of servicing things that a pilot can do (change plugs? top-up undercarriage oil? etc), etc, etc
(TBH lots of this should have been covered on the type cvx and, by the time you've completed a CPL course, you really should know what the various aerials are for).
There's a CAA booklet giving suggested questions for examiners, it's probably on the website if you poke around.
HFD