CREATE TABLE table_20238 ("Date" TEXT, "Cover model" TEXT, "Centerfold model" TEXT, "Interview subject" TEXT, "20 Questions" TEXT, "Pictorials" TEXT)

What's the subject of 20 questions in those issues where Jillian Grace is the centerfold model?
SELECT "20 Questions" FROM table_20238 WHERE "Centerfold model" = 'Jillian Grace'
SELECT "20 Questions" FROM "table_20238" WHERE "Centerfold model" = 'Jillian Grace'