하나 is composed of 하(다)+나 나 is an ending particle used for question. There are two main usages. First, asking to junior in a casual form. Second, asking to oneself with with supposition. Generally, use 해요 when asking to someone else. Use 하나 when asking to yourself.

The 하나 one is asking a question in a casual form :) it's probably not a good idea to use 나? with an elder, someone you don't really know, someone of a higher position , someone even a bit older than you who you are not friends with