If my reputation is under 2k and someone edited my answer. If I reject the changes that the message appears that
"You can receive the edit after 2K reputation".
What does that mean?
I'm a little unsure of what you're seeing, since the exact phrase you've quoted doesn't appear anywhere that I know of, but from what I can tell...
It sounds like you're getting the "you need 2,000 reputation to review suggested edits" message. If somebody suggests an edit to your post while you have less than 2,000 reputation, you can review the edit - either approving it, applying it to your post, or rejecting it so that it doesn't apply. After you're done, the system will try to move you to the next item in the review queue. However, since you need 2,000 reputation to review suggested edits on other people's posts, it tells you that need 2,000 reputation to continue reviewing.