Refer to figure.
Learning Objective 021.12.02.01.02: State that two discharges must be provided for each engine (see CS 25.1195(c) Fire-extinguisher systems). [Note: the regulation changed slightly and it is now CS 25.1195(b)]

CS 25.1195 Fire-extinguisher systems

(b) The fire-extinguishing system, the quantity of the extinguishing agent, the rate of discharge, and the discharge distribution must be adequate to extinguish fires. It must be shown by either actual or simulated flight tests that under critical airflow conditions in flight the discharge of the extinguishing agent in each designated fire zone specified in sub-paragraph (a) of this paragraph will provide an agent concentration capable of extinguishing fires in that zone and of minimising the probability of re-ignition. An individual ‘one-shot’ system may be used for fuel burning heaters, and other combustion equipment. For each other designated fire zone, two discharges must be provided each of which produces adequate agent concentration. (See AMC 25.1195(b).)

As you might notice from your teaching syllabus and other questions, the majority of twin engine jets have 2 BOTTLES of fire extinguisher for use on the main engines, and each can be sent to either engine, meaning that each engine has 1 BOTTLE, but 2 DISCHARGES available.