In my opinion, Ethics is best covered in the CFAI curriculum.
The more cases/scenarios your read and understand from the curriculum, the more you develop your ability to apply the Code of Ethics and the Standards of Professional Conduct to a set of facts.
The CFAI Readings (R1,R2) on Ethics are from the Standard of Practice Handbook. So they are essentially the same. This is the core material for Ethics. However, at the back of the Standards of Practice Hanbook you get a sample test as well. I can’t recall if these questions were also repeated in the CFA text, but in any case here is a link to the Eleventh Edition of the Standards of Practice Handbook
Agreed. Ethics should be read directly from the curriculum. My best advise is to read it early in your study plan, refer to it if needed when working practice quesitons and mocks, then fully read it again 2-3 nights before the exam.