My impression is that you can take the ideas and principles of Eneagrams and research the subject as you see fit. A brief trawl around the key resources related to this shows nothing to state that the concept of Eneagrams or Eneagrams themselves are protected in any way. A bit like astrology, kabbalah and similar, it's a belief system of sorts and thus open to individual interpretation.

That's just my uninformed opinion.

A couple of paragraphs from Stanford University - Copyright and Fair Use [fairuse.stanford.edu].

Copyright shelters only fixed, original and creative expression, not the ideas or facts upon which the expression is based. For example, copyright may protect a particular song, novel or computer game about a romance in space, but it cannot protect the underlying idea of having a love affair among the stars. Allowing authors to monopolize their ideas would thwart the underlying purpose of copyright law, which is to encourage people to create new work.

For similar reasons, copyright does not protect facts -- whether scientific, historical, biographical or news of the day. Any facts that an author discovers in the course of research are in the public domain, free to all. For instance, anyone is free to use information included in a book about how the brain works, an article about the life and times of Neanderthals or a TV documentary about the childhood of President Clinton -- provided that that they express the information in their own words.

Usual disclaimer applies: I am not offering legal advice, please do seek legal advice.

Syzygy