How do I read Infolog messages in X++?

You can inspect the Infolog data with SysInfologEnumerator.

SysInfologEnumerator enumerator =
    SysInfologEnumerator::newData(infolog.infologData());

while (enumerator.moveNext())
{
    SysInfologMessageStruct message =
        new SysInfologMessageStruct(enumerator.currentMessage());

    info(message.message());
}

This is useful when you genuinely need to inspect or capture messages programmatically.

I would not use it just to read every Infolog message and then write the exact same messages back to the Infolog again.