書くの

writing

→ 書く
phrase Common #3,703
writing の can turn 書く into “writing” or “the act of writing.” After an inflected verb, it can also add an explanatory tone or appear in a question.
JA: 日記を書くのが好きです。
EN: I like writing in my diary.

❝ゆり❞だって❝ゆり❞ってどんな字書くの?

How do you spell "Yuri"?

— 万引き家族 (2018)

起きたことを書くの。

I’m writing about what happened.

あなたはバカで腐った貴族についての記事を書くの?

Are you going to write an article about stupid, corrupt nobles?

— 甘い生活 (1960)

書くの。

I’m going to write it.

名前はどう書くの?

How do you spell your name?