(that) which is; in capacity of ... should
This N1 pattern expresses that someone, in their capacity as a certain kind of person, has an expected duty or behavior.
This pattern is used to say that because someone is (a certain kind of person), they should do something or have a certain quality. It sounds formal and is often found in written statements, speeches, or company rules. It carries a strong sense of duty and expectation.
The phrase たるもの is a set expression meaning 'as one who is ...' and is used to remind someone of their responsibility. For example, 教師たるもの means 'as a teacher' with the nuance that a teacher has certain obligations.
You can also use たる alone with a noun, but it is rare and literary. In everyday conversation, this pattern sounds stiff, so it's better to use it in written or formal contexts.