In China, the currency is the CNY (Chinese Renminbi). The exchange rate is around 1€ to 7.56 CNY (as of 05/2020). The CNY is not a freely convertible currency, so you cannot get it at every bank in Europe. The exchange rate, which is determined by the Bank of China, can be observed under the following link: http://www.boc.cn/sourcedb/whpj/enindex.html
However, we recommend withdrawing a larger amount of CNY from an ATM with all major credit cards or debit cards after arriving in China. Our on-site tour guide is happy to help. Due to the often very poor exchange rate for the CNY in Europe, it is not worthwhile to exchange significant amounts of CNY in Europe. There are also many ATMs in Lhasa where you can withdraw money. Our experience shows that the majority of our participants spend around 20€ a day.