What is the prefix of kindness?

There isn't a single, universally recognized prefix for "kindness." However, you could use prefixes like:

* Bene-: Meaning "good" or "well," as in "benevolent" (characterized by or expressing goodwill or kindly feelings)

* Kind-: This is the root word itself, and could be used in combinations like "kindhearted" or "kindly"

* Human-: Meaning "relating to or characteristic of humans," as in "humanity" (the quality of being human; human nature)

Ultimately, the choice of prefix would depend on the specific context and the desired nuance.