It is difficult to answer this question without knowing specifics about the law involved. However, generally speaking, a country’s laws are applicable to its citizens and foreign nationals who are present in its jurisdiction. Putting bounties on pro-democracy activists, including American citizens, would be illegal under international laws, including the UN Universal Declaration of Human Rights. However, if Hong Kong is operating under a China-imposed law that allows such actions, then it would be legal for Hong Kong to do so.
