Read as much as a you can on big aircraft systems ... it will all help. The various notes and practice exams are helpful but only that.
I think it dates back to the days when ATPL was "senior commercial" and candidates were expected to be rated on and know a range of big aircraft. Many of the questions would be trivial if you're familiar with the type ...
"what colour is the active flight plan leg on the FMS" ... well I always follow the pink line, so it must be ... answer B. Or
"can you reengage the type X generator in flight" ... no, the engineer screamed when I went to do that, so I guess not.
There are various books and websites (free
) with descriptions and diagrams appropriate for the subject - study these lots and most of the questions will be sensible. (But don't bother memorising numbers, it's mostly questions testing your understanding, not your memory.)