Knowledge is the output of a person and their expertise and perspective, irreducibly. In this case, they seem to know something of what they're talking about:

> Starting 2022, I am now the John Cardinal O’Hara Professor of Logic at the University of Notre Dame.

> From 2018 to 2022, I was Professor of Logic at Oxford University and the Sir Peter Strawson Fellow at University College Oxford.

Also interesting:

> I am active on MathOverflow, and my contributions there (see my profile) have earned the top-rated reputation score.

https://jdh.hamkins.org/about/