As an Agile Coach I was asked to run a workshop to assess the agile mindset and diagnose the gaps to be addressed.
Curiously, almost everybody is honestly convinced to be already and truly agile.
Challenging (or proofing) this belief was a very insightful experience.

I prepared this experiment referring to the 4 values of the original Agile Manifesto for Software Development, which could immediately serve as a Prototype already workable to be eventually inspected and adapted for the Sustainable Agility paradigm.

Let me know if interested.
In my experience, the optimal number of participants is between 6 and 10 to let enough time for the discussion.
Ideally, participants should not be all-knowing gurus (which of course have a solid and weathered Agile mindset not needing to be verified) but people with a good attitude towards agility but still with doubts, questions and old habits to discard.
If you don't have a such "ideal" target audience, try to simulate the situation by putting yourself "in their shoes". (I'm sure you've met such characters many times...)