Questions & Answers about Мой друг живёт в далёком городе.
In Russian, possessive pronouns must agree in gender, number, and case with the noun they describe.
Друг is a masculine noun in the nominative case, so you must use the masculine nominative form мой.
You would use моя with feminine nouns (e.g. моя сестра) and моё with neuter nouns (e.g. моё окно).
Друг is grammatically masculine and usually refers to a male friend.
For a specifically female friend, Russians normally say подруга.
So for a female friend, you’d say: Моя подруга живёт в далёком городе. (feminine моя + feminine подруга).
For plural friends, you use друзья: Мои друзья живут в далёком городе.