At the ISS, it will most likely fall under the United Nations. If that is not the case, say if the judiciary situation involves a Russian and Japanese cosmonauts in an American module, the jurisdiction will fall under a united front of all the space agencies (Canadian Space Agency, ESA, JAXA, NASA, and Roscosmos) involved with the station. Or if just one module + crew is concerned with the situation, the country that owns it will exercise their jurisdiction.
