Use RAMCategory.getSubCategories() and RAMCategory.getSubCategory(String subCategoryName) methods to fetch all the subcategories from the within a category. If this schema was fetched through RAMAsset.getCategorySchemas() or RAMAsset.getCategorySchema(String schemaName) it will only contain the subcategories that are set or contain subcategories set on the asset.
//Get all sub categories for a category
RAMSubCategory[] subCategories = (RAMSubCategory[])modelCategory.getSubCategories();
//Get a sub category by name
RAMSubCategory foreignSubCategory = (RAMSubCategory)modelCategory.getSubCategory("Foreign");
//Get a sub category given a path to from the category
RAMSubCategory camrySubCategory = (RAMSubCategory)modelCategory.getSubCategory("Foreign/Toyota/Camry");
//Get a sub category given a path from a sub category
RAMSubCategory accordSubCategory = (RAMSubCategory)foreignSubCategory.getSubCategory("Honda/Accord");