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.
UPDATE: Thomas Edison's carbon coated bamboo filament lightbulb might work. He already did the hard work inventing it. Not sure how available bamboo was in medieval Europe (assuming you're thinking about Europe). But you could do the research in your current timeline before sending it back to the past. There must be an alternative available to your intended audience.
The vacuum inside the bulb could be more or less achieved. A metal box sealed with wax, and emptied of air by a bank of bellows with non return valves. Might be tough to get a complete vacuum, but you'd get a fair way. Maybe oxen turning a geared wheel linked to a cam shaft to keep the bellows going?
Have the bulbs and filaments all set up inside the box. Set leather gloves into the side of the box to work on the bulbs inside. Leather would probably leak air into the box, but keep those oxen moving. Promise them a bonus if they make budget.
Using the gloves (they'd need to be tight but supple gloves to counter the ballooning that would happen from the negative pressure inside the box, maybe banded with wire), assemble the bulbs. All you'd need to do is attach the glass bulbs onto the bases with the filaments already attached.
One problem would be to attach the bulbs and bases together. With the electricity you are already producing, it might be possible to have a soldering iron inside the box. Otherwise some kind of glue, maybe made from boiled sinew, potato starch, whatever.
Edison got around 1200 hours of life out of his bamboo filament bulbs.