The most common and most likely answer to this crossword clue is the 11 letter word IGNORAMUSES
I've seen this crossword clue in Financial Times
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More clues leading to the result IGNORAMUSES
Buddy explains!

The straight part
We know that "People knowing nothing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case people knowing nothing = ignoramuses.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IGNORAMUSES mean?
IGNORAMUSES noun- A totally ignorant person—unknowledgeable, uneducated, or uninformed; a fool.
- A grand jury's ruling on an indictment when the evidence is determined to be insufficient to send the case to trial.