1. Hanbok is Korean traditional dress.
2. Hanbok is a Korean traditional dress.
3. Hanbok is traditional Korean dress.
4. Hanbok is a traditional Korean dress.
(Which one is correct?)
First some questions: What is Hanbok? Is it a particular style of clothing? Or is it a specific article of clothing?
If it's a style of clothing, then 1 and 3 are correct; 3 is the better of the two.
If it's a particular article of clothing, then 2 and 4 are correct, and 4 is better.