In the question "Do you know my friend Steven Jonsen?" is the grammar correct?
There is some ambiguity, in my opinion, if you add a comma. It could mean that you are talking to someone called "Steven Jonsen" and you are asking him "Do you know my friend?" I realise that is a little unlikely. However, without the comma, it is clear that you are talking about "my friend who is called Steven Jonsen".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Not a teacher nor a native speaker.
I suppose the punctuation rules are the same in the whole world. In my language a comma after friend is required.
Please, correct all my mistakes. I should know English perfectly and if you show me my mistakes I will achieve my dream a little bit faster. A lot of thanks.