Short answers, pulled from the story.
The oldest directly dated skull cup comes from Gough's Cave in Somerset, England, and has been dated to approximately 12,750 BC (14,700 cal BP). It was produced by people of the Magdalenian culture during the Upper Paleolithic.
A kapala is the Sanskrit name for a skull cup used in Buddhist tantric and Hindu tantric rituals in India and Tibet. The identity of the skull's original owner is not considered significant; the object's ritual function is what matters. Hindu deities such as Kali are depicted holding a kapala filled with human blood, and many elaborately carved kapalas survive, mostly in Tibet.
According to the Han shu, the skull of the Yuezhi king, killed by Laoshang around 162 BC, was later used during treaty negotiations with Han China. Chinese ambassadors drank blood from the skull cup alongside Xiongnu chiefs to seal the agreement during the reign of Emperor Yuan of Han, who ruled from 49 to 33 BC.
The contemporary chronicle Shincho Koki and the secondary source Azai Sandai Ki confirm that Nobunaga displayed lacquered, gold-painted skulls of Asakura Yoshikage, Azai Hisamasa, and Nagamasa at a feast in the lunar New Year of 1574. However, neither document states that he actually drank sake using the skulls as cups, and whether his intention was cruelty or respect for his enemies remains disputed.
Skull cups are distinguished from ordinary skulls by two physical features: cut-marks left from removing flesh and deliberate working to produce a regular lip around the rim of the calvaria. A skull lacking these marks cannot reliably be identified as a vessel.
Byron had a skull found by his gardener at Newstead Abbey polished to a tortoiseshell-like finish and mounted as a drinking cup. He filled it with claret and passed it among the Order of the Skull he founded at the Abbey. He also wrote a poem about it titled "Lines Inscribed upon a Cup Formed from a Skull", which he later described in conversation with Thomas Medwin.