CREATE TABLE table_1566852_6 (centerfold_model VARCHAR)

What's the subject of 20 questions in those issues where Jillian Grace is the centerfold model?
SELECT 20 AS _questions FROM table_1566852_6 WHERE centerfold_model = "Jillian Grace"
SELECT 20 AS "_questions" FROM "table_1566852_6" WHERE "Jillian Grace" = "centerfold_model"