Where to send a deceased person’s passport?

You can return their passport for cancellation with a copy of their death certificate the Consulate General in Shanghai:

Suite 700A (West Tower)
Shanghai Centre
1376 Nanjing Road West
Shanghai 200040
People's Republic of China

爱尔兰驻上海总领事馆

南京西路1376号上海商城西峰700A

邮编200040

中国·上海