According to this news release (written in Traditional Chinese) , the "Treaty of Nanking" is kept by the ROC hence Hong Kong should be returned to ROC. But we all know that in year 1997, Hong Kong was returned to PRC instead.
Why?
The United Kingdom withdrew its recognition of the Nationalist government and recognized the PRC on January 6, 1950. In 1962 the UK switched sides in the UN and started voting for the PRC to be seated in the UN and the ROC excluded. The UK closed the provincial consulate that had operated in Taiwan in 1971, acknowledging the PRC position that Taiwan is a province of the People's Republic of China. Thus the UK had no legal argument to return Hong Kong to the ROC. (The Taiwanese army, in any case, has never aspired to do more than prevent the PRC from invading and occupying Taiwan, defending Hong Kong from an enraged PRC would be utterly beyond them.) Margaret Thatcher briefly considered keeping Hong Kong Island and Kowloon after the New Territories were returned, but was quickly informed by the civil service that this was completely unrealistic and unworkable. The PRC, which had never recognised the 'unequal treaties' as legitimate, wanted all of Hong Kong back and the 1997 date was a piece of facesaving that enable the UK to pretend the return was their decision.
https://books.google.com/books?id=PJSkDQAAQBAJ https://books.google.com/books?id=SckYDQAAQBAJ