Knock Knock, a five-year-old gift and stationery company, has created its own genre of witty, whimsical, and fun products. Founded and headed by Jen Bilik, Knock Knock, a division of Who's There, has earned kudos and an enthusiastic base of retailers who are charmed by the contemporary wit in vintage design. Launched in 2002, with 13 products, Knock Knock now offers several hundred items, including a new line of books.