Cake calls for flour but doesnt specify self-rising or all-purpose. It has salt baking soda and buttermilk. Which flour does it mean?

Building on CV's answer, I would say a recipe never calls for self-rising flour, unless it says to use it. Self-rising flour is just flour that has baking powder and salt already mixed in. Since it is often made with lower gluten flour you could mix equal measures of AP & cake flours. Most recipes I see just call for all 3 separately. In your case the baking soda will provide the rise in combination with the acid in the buttermilk.

If a recipe calls for flour yet doesn't specify the type, the wisest choice is all-purpose flour.