Is the word truthfulness a prefix or suffix?

"Truthfulness" is neither a prefix nor a suffix. It's a noun.

Here's why:

* Prefixes are added to the beginning of a word to change its meaning (e.g., "un-" in "unhappy").

* Suffixes are added to the end of a word to change its meaning or grammatical function (e.g., "-ness" in "happiness").

"Truthfulness" is a word on its own, meaning "the quality of being honest and truthful."