In the Hebrew, Chanukah is pronounced with the letter chet. The chet’s "ch" sound is not enunciated like the "ch" in child; rather it’s a guttural, throaty sound—like the "ch" in Johann Bach—which does not have an English equivalent. The letter "H" is the closest, but it’s not really it. So while some people spell and pronounce it "Chanukah" and others settle for "Hanukkah," they really are one and the same.
Photo of dreidels courtesy Wikimedia.