The right to public hearings (subsumed in the right to fair trial) is enshrined in Article 10 of the Universal Declaration of Human Rights.
Human Rights Committee (if the optional protocol is ratified by the state)
Special Rapporteur on the independence of judges and lawyers
Special Rapporteur on the human rights of migrants
Special Rapporteur on the situation of human rights and fundamental freedoms of indigenous people
African Commission or Court on Human Rights and Peoples’ Rights