In the market for a Hollywood home? If you’re Claire Danes or Leonardo DiCaprio, the search for the ideal domicile begins with the answer to the trivia question ”Who’s the girl in the Knack‘s 1979 hit single?” — Real estate agent Sharona Alperin, 37, is, indeed, that Sharona. Working out of the Sunset Boulevard office of the Dalton, Brown, and Long firm, Alperin, just 17 when she inspired the lecherous No. 1 new-wave ditty, has avoided obscurity by becoming a top brokerata.