Q:

How to agree with a negative statement: with "yes" or with "no"?

This question here asks about answering negative questions:

How to answer a negative question in English?

I have a completely different question. I want to know:

how do we agree or disagree with negative statements in English.

Example:
––This is not a duplicate question.
––Yes, it is a new one.
or
––This is not a duplicate question.
––No, it is a new one.

A:

The standard way is to clarify your answer by rephrasing the question rather than only saying "no" or "yes".

A - This is not a duplicate question.
  B - Yes, it is [a duplicate question].
A - This is not a duplicate question.
  B - No, it is not [a duplicate question].

