A matter of a taste, not a substance. Form "somebody" fits better if you talk about a single person. "She speaks to nobody", and when there exist relation to a group "I asked everybody, but no one knew the answer" sound much better. It is fully acceptable to use them use them interchangeably. "I asked everyone, but nobody knew the answer" just does't sound smoothly.

I think there is no difference. They have the same meaning. E.g. Nobody knows/ No one knows

Hello. Kat .and Piotr. I'm very sorry I'm so late about my answer. I was so busy.! XD Thank you very much for your answer. it's so helpful to me.