The book would have to be written in a language that the recipient could understand. Not just the words, but the concepts.
It would need a primer, an explanation of the concepts starting with "This is a copper wire, and this is how you connect it to another copper wire."
You wouldn't necessarily have to explain how or why it all works (maybe later in the book), just a dumb diagram with plenty of visual instructions.
Concepts such as magnetism would have to be worked around for the motor/generator, but that is easy enough.
The lightbulb would be more difficult than the motor (electric motor and electric generator are essentially the same thing).
I would guess that an alchemist or a priest would be the best person to hand the book to in medieval times in Europe. The alchemist would be used to working with different minerals and metals, and priests were often the most educated. A blacksmith would be able to help.
The moslem world was flourishing during those times, and they had a highly advanced grasp of mathematics and science at that time.
During the renaissance, your one-stop-shop would have been Leonardo Da Vinci, the original 'renaissance man'. Jack of all trades, and master of them as well.
I think that if the book were written the right way, it would be possible for someone in those times to put it all together.
If WW2 prisoners of war could build functioning radios out of bits of junk found around the camps, and people 2,000 years ago could make a battery (although the usefulness of the Baghdad battery is disputed), then it would be possible to build some simple electrical devices.
As to who would make the best usage for humanity, I couldn't say. After the Roman Empire, Europe was in chaos. Splintered kingdoms who were pretty much all in it for themselves.
But I think Leonardo would be your best bet.