Based on the origin of the word knowledgeable (knowledge, knowable), the word part know probably means
a. to perceive or understand - she was the only person to know what really happened that day.
b. to disagree, to deny - her brother was always negative, he never wanted to know the truth.
c. to disagree with - he always said know when she suggested a destination for their vacation.

Hi, the correct answer is A. That is the only option where the verb "know" is used in the meaning which is explained. To perceive or understand means to know or realize something, in this case "what really happened that day". "To not know" doesn't necessarily mean "to disagree, to deny", given in the second example. And in the final example, "know" is used incorrectly instead of "no".