The preferred oxygen delivery device to use when providing emergency oxygen to a non breathing person is a:

ventilation mask (with oxygen inlet) is The preferred oxygen delivery device to use when providing emergency oxygen to a non-breathing person.
A ventilation mask with an oxygen inlet is consist of a pump that allow another person to pump the air into the non-breathing person's lung.
Other form of oxygen delivery device require the user to directly breath in to the device, which will be impossible of that person is non-breathing condition.