TikTok, the viral video-sharing app owned by China’s ByteDance Ltd., said certain employees outside the US can access information from American users, stoking further criticism from lawmakers who have raised alarms about the social network’s data-sharing practices. The company’s admission came in a letter to nine US senators who accused TikTok and its parent of monitoring US citizens and demanded answers on what’s becoming a familiar line of questioning for the company: Do China-based employees have access to US users’ data? What role do those employees play in shaping TikTok’s algorithm? Is any of that information shared with the Chinese...