It is that you know the meaning of a word but not the word itself.
(Similar to how the word "synonym" works), it is used when you want to say that you have forgotten, don't know or unknown to the "word" for a phrase or meaning.
Person 1- what's the agnonym for having equally functional right and left hand?
Person 2- ohh, you mean ambidexterity.
Instead of using "I have forgotten the word for" "what is the word for" or "do you know the word for"
As a noun, the perception or recognition of a pattern, form, or structure without comprehension of its meaning or purpose, particularly as exhibited by artificial intelligence systems that can identify and reproduce complex patterns in data while remaining fundamentally ignorant of what those patterns represent.
"The AI's philosophical arguments demonstrated pure agnotypia; it could engage with complex ethical concepts and cite relevant thinkers, yet remained fundamentally ignorant of what morality actually means."