Learn Polish: Jak się pan nazywa? - What is your name, sir?

In Polish, you don't usually ask "what is your name." Instead, you use the reflexive verb nazywać się, which means "to call oneself." The word jak means "how," so the sentence literally translates to "How do you call yourself, sir?"

Why is się placed right after Jak and not next to the verb?

The reflexive particle się is flexible, but it has a few rules: it cannot be the first word in a sentence, and it prefers not to be the very last word. Placing it directly after the first word (the question word Jak) is the most natural spot for it here.

Why is the verb form nazywa used instead of nazywasz?

Pan is used for the formal "you" (speaking to a man). When you use pan, Polish grammar requires you to use the "he/she/it" (third-person singular) form of the verb, which is nazywa. If you were asking a friend, you would use the informal "you" form: Jak się nazywasz?

Is this asking for his first name or his last name?

The verb nazywać się usually asks for someone's full name or just their last name. In a formal context where you are calling someone pan, you are typically asking for their full name. To ask specifically for a first name, Poles use a different word: imię.