Boths are correct. And we use them. But mostly while in a introduce conversation "Ne iş yaparsın?" is preferred.

"Senin işin nedir?" or "Ne iş yaparsın?" sounds unnatural and even maybe a little bit rude to me. i would prefer; "ne iş yapıyorsunuz?" or "mesleğiniz nedir?"

In addition to the above, a few sentences can be said. You say "Ne işle meşgulsünüz?" you met a new person. A little more practically, there are those who say, "Ne işle iştigal?" But the standard question is: "Mesleğiniz nedir?" or "Ne iş yapıyorsunuz?" The present time pattern in the second sentences can actually cover both the present continious time and the present time.