verb + の + ですか　？（what is the の doing?)
I am trying to understand why this hiragana is used to ask certain types of questions.

Like this:

彼らは何を見ているのですか

あなたはどうして笑っているのですか

友達はどこに行くのですか

is there a difference between this and saying something like:

友達はどこに行きますか

Thank you :D

Question

verb + の + ですか　？（what is the の doing?)
I am trying to understand why this hiragana is used to ask certain types of questions.

Like this:

彼らは何を見ているのですか

あなたはどうして笑っているのですか

友達はどこに行くのですか

is there a difference between this and saying something like:

友達はどこに行きますか

Thank you :D

Answer

It implies that you are asking for a reason. 何やってるんですか？For example. It opens up for the other person to explain. Without の/ん/なん　it's just a statement. That is the essence of it.

집에서 편안하게 언어를 배울 수 있는 기회를 놓치지 마세요. 경험 많은 강사진을 살펴보고 지금 바로 첫 수업을 신청하세요!