There are no restrictions on who can attend an event.
However, if you are not in possession of a UN badge should register to the event of your choice on the UNOG website.
Register for Cultural Activities here
Register for Library Events here
Please bring a valid ID on the day of the event to the UN visitors entrance the Pregny Gate, located at 8-14 Avenue de la Paix, 1211 Geneva 10, in front of the International Committee of the Red Cross building. (Please, see map here)