sumimasen / suimasen= excuse me
anatano = your
namae = name
nan = what
nandesuka = what is
In reality, it is rare to ask someone’s name like this. Imagine you are meeting someone for the first time, you would probably introduce yourself by telling your name and for sure the person you are meeting with would do the same.
This phrase introduced here is more like a script in an adventure movie, where the hero/heroine of the movie would say right after he/she is rescued by a mysterious character.