"You know me well" conveys a different meaning.
"You get me?" or "Do you get me" Is often used in angry or confrontational contexts. After harsh criticism of another person or persons, the speaker may conclude with "Do you get me?" or "Do you get my meaning?" That invites the hearer to say yes or no, or to show compliance or disrespect. Silence may be regarded as disrespect or ignorance.
“You understand me” and “You know me well” are not questions but are affirmations or statements. They affirm that you are well acquainted with me. It is critical to distinguish between the use of a statement and the use of a question. The meanings change with the intonation.