Use RAMAsset.getCategorySchemas() and RAMAsset.getCategorySchema(String schemaName) methods to fetch all the category schemas and the category trees that have subcategories set.
//Get All Set Category Schemas
RAMCategorySchema[] setSchemas = (RAMCategorySchema[])newAsset.getCategorySchemas();
//Get a set Category Schema by name
RAMCategorySchema automobilesSchema =
(RAMCategorySchema)newAsset.getCategorySchema("Automobiles");