I am doing well

The answer for the question, "How are you doing?" is not:

I am doing good. (INCORRECT)

The correct answer is:

I am doing well. (CORRECT)

am I not vs. aren’t I

The incorrect expression "..., aren’t I?" is often used instead of "..., am I not?" in conversations.

Example:

I’m going with you to the movies, aren’t I? (INCORRECT)

I’m going with you to the movies, am I not? (CORRECT)

One of my ...

Learn by examples:

Example 1:

One of my friend lives in North Vancouver. (INCORRECT)

One of my friends lives in North Vancouver. (CORRECT)

Example 2:

I saw one of your friend yesterday. (INCORRECT)

I saw one of your friends yesterday. (CORRECT)