The dictionary lists "-ever, at all, -soever" as the definition of ajn.

I would just like to clarify the use of this word, as it appears often after correlatives in an almost needless way, such as in the phrase:

"Li scias nenion pri io ajn."

To me "io" already signifies "anything". The use of ajn seems strange. I wouldnt want to overuse it.

Is it merely a stylistic approach in many cases, as if to apply more force to the idea of "nothing" or "anything"?

ajn adds more force.

"io" means both "something" and "anything". But "io ajn" means only "anything", definitely not "something".

In English we add similar emphasis with "at all".

I have nothing = Mi havas nenion
I have nothing at all = Mi havas nenion ajn

Do you have anything? or Do you have something? = Ĉu vi havas ion?
Do you have anything at all? = Ĉu vi havas ion ajn?

The main difference is that Esperanto can use "ajn" with correlatives that don't ever get
"at all" in English.

Kion ajn vi havas, mi ne zorgas. = Whatever at all you have, I don't care.