Short answers, pulled from the story.
The donkey was domesticated in Africa approximately 5,000 years ago, with the earliest domestication believed to have occurred in Nubia. Remains of domestic donkeys dating to the fourth millennium BC have been found at Ma'adi in Lower Egypt, and genetic evidence indicates a separate domestication event among Cushitic-speaking peoples in the Horn of Africa and along the Red Sea Hills.
About 41 million donkeys were reported worldwide as of 2006, down from 43.7 million in 1995. About 96 percent live in underdeveloped countries. China, once the country with the most donkeys at 11 million in 2006, had seen its population drop to 3 million by 2017.
Ejiao is a gelatine produced by boiling donkey skins, used in traditional Chinese medicine. At October 2017 prices it could sell for up to $388 per kilogram. Rising Chinese demand for ejiao contributed to a sharp fall in China's own donkey population and increased pressure on African donkey populations, prompting The Donkey Sanctuary to warn in 2019 that the global population could be halved within five years.
A mule is the offspring of a male donkey (jack) and a female horse (mare), while a hinny is the offspring of a male horse (stallion) and a female donkey (jenny). Mules are generally considered more easily handled and physically stronger than hinnies, making them more desirable for breeders. Both hybrids are almost always sterile.
The first donkeys reached the Americas on the ships of Christopher Columbus's Second Voyage, landing at Hispaniola in 1495. The first animals to arrive in what is now the United States may have crossed the Rio Grande with Juan de Onate in April 1598, spreading northward through missions and mines. Donkeys were documented in what is now Arizona in 1679.
The kunga was a hybrid animal produced in the Syrian and Mesopotamian kingdoms during the second half of the third millennium BC, making it the earliest documented example of human-directed animal hybridization. It was bred at Nagar (modern Tell Brak) by crossing a captive male Syrian wild ass with a female domesticated donkey. Kungas pulled battle wagons and royal chariots and were valued enough to be sacrificed and buried alongside high-status people.