Which Chinese highway, part of the G318, connects Lhasa to the Nepal border?

The Chinese highway connecting Lhasa with the Nepal border as part of G318 is the Friendship Highway.

Also called the China–Nepal Highway, it runs roughly 800 kilometres from Lhasa to the Sino-Nepal Friendship Bridge near Zhangmu and Kodari. Its Chinese route-number identity is the westernmost section of China National Highway 318, whose much longer alignment begins in Shanghai.

The route passes through Shigatse and near the northern approach to Mount Everest before crossing several exceptionally high passes. Gyatso La, at about 5,260 metres, is the highest pass on the road; the highway crosses three passes above 5,000 metres before descending sharply toward the border.

The Yunnan–Tibet and Sichuan–Tibet highways are different routes entering Tibet from the east and south-east. The Karakoram Highway is another high-altitude international road, but it connects China with Pakistan rather than Nepal.