For the situation what you mentioned, A: Do you know that? B: Of course I know. A: 那个你知道吗？ B: 我当然知道了。 It is kind of weird to answer "当然，我知道。" in this situation. Another example, "of course it is" = "这当然是(这样)的了". subject + 当然 + verb + other things. Generally it's like this, as for the structure.

Bonjour， je ne suis pas un expert en chinois (en fait, je ne suis qu'un débutant), mais je pense que dans ce cas je peux répondre à ta question. 是的, c'est "oui". Tout simplement. Ça n'as pas le sens de "bien sûr". En fait, si tu veux dire: "Oui, bien sûr!", tu devras dire: "当然是的!"

Hi,there. When you answer the question-----:你知道吗? ,you can say"Of course, I know".But you should say "我当然知道"instead of "当然，我知道"。You know,this is the problems of language order. You can also say"是的". There is a little different between these sentence.When you say"我当然知道",it means you answer the question with confidence and you believe in yourself . "是的"just likes "yes". I will show you some example as follow: 你爱他吗？是的/当然。（Do you love him? Yes/Of course） 我可以把真相告诉他吗？是的/当然可以。（Can I tell him the truth? Yes/Of course ，you can） 你可以教我跳 dougie吗？当然。（Ｗould you teach me how to dougie? Of course.） When someone ask you for help,I recommond you to use "当然可以"。 For example,,Li qin,可以帮个忙吗？当然可以。（Can you give me a hand? Of course.） At this situation,people will know that you are willing to help him/her. That's all .Hope it can help you.Enjoy learning Chinese.

当然is used to answer the question that is sure ,like more certainly,是的is answer to question about "whether"

They both mean the same. A:你知道吗? ---------当然，我知道。 B:你知道吗? ---------是的，我知道。