Sister City Transparency Act This bill requires the Government Accountability Office to study the activities of sister city partnerships involving foreign communities in countries that received a score of 45 or less on Transparency International's 2019 Corruption Perceptions Index. A sister city partnership is a formal agreement between a U.S. community and a foreign community that is recognized by Sister Cities International and that is operating within the United States. Among other elements, the required study must (1) identify oversight practices that U.S communities implement to mitigate the risks of foreign espionage and economic coercion within sister city partnerships, (2) assess the extent to which U.S. communities ensure transparency regarding sister city partnership contracts and activities, and (3) review the range of activities conducted within sister city partnerships.