"I do not know what to buy."
Translation:Mi ne scias, kion aĉeti.
Why is konas not accepted, when you buy something you usually know what to buy from experience and not as a fact?
That's a different meaning.
"Mi ne scias, kion aĉeti." = I am sitting in front of an empty shopping list and I am wondering what to put on it.
"Mi ne konas, kion mi aĉetas." = I am buying something, without knowing what it is.
When I read the question, I imagined standing in a store with all sorts of things on the shelves, and I could not decide which one to buy, because there were too many choices. This type of confusion seems to me to be not very intellectual and more suitable for konas than for scias. But I got this as multiple choice and there was no konas there, only scias.
After a bit I realized that in spanish I actually do make the difference between "saber" -- "scii" and "conocer" -- "koni", which made it quite easy for me. It is quite odd, but to put it in a very rough way, koni seems to be when you have a more personal connection, like, you have met that information somewhere, as opposed to possessing that information
Another strange example is that you Know "scias" how to do it. But you Know "konas" a way to do it.
Also.... think of "konas" as "I am acquainted with"