Should it be the closure plug from Knauf or does it not matter?
It does not matter. There are dozens of suppliers – but the workers should use the plugs intended for the system (Knauf was an example – for the Warm Wall system) ==> it is only about the warranty. Otherwise, it really does not matter. It is usually PUR soft foam. You compress it by hand, insert it into the hole, and then it immediately expands again (like a compressible tape/window tape). This then counts as wind-driven rain tight.