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1.
To know knothing is to misspell 'know nothing', so it means the same thing as to 'know nothing'.

It is rumored to have originated in a Twitter conversation by MiriIsACat in 2014.
Girl: "You know knothing"
Guy: "Know knothing, KNOTHING. NEVER FORGET. #KNOWKNOTHING2014"
by John W.W. February 28, 2014