Look up lists of Jewish celebrities, available online. Spiritus-Temporis.com has an alphabetical listing, while Wikipedia lists Jewish actors and actresses by year of their birth, with the youngest celebrities being born in the 1990s.
Check the lyrics of Adam Sandler's Hanukkah songs to see if the celebrity you're curious about is listed. At the very least, these songs can give you a chuckle and will inform you about other celebrities who are fully or partially Jewish.
Check with the celebrity's publicist or fan club director if you can't find information on his religion online. Decades ago Hollywood stars would hide their ethnicity because Antisemitism was so rampant, but today most people are happy to disclose even if they are 1/4 Jewish.
Search for famous people who follow the Kabbalah. Kabbalism is related to Judaism but not quite the same thing--you must be born Jewish but Kabbalah is a philosophy that originated with Jewish scholars. Kabbalah-following celebrities like Madonna are not necessarily Jewish, but it's still amusing to see the link between the stars and the Jewish culture.