The correct spelling is חנוכה
The first letter is ח called Ḥet and is pronounced like a ch where the c is like a bit of phlegm in your throat.
The next letter is נ called Nun and is pronounced like N.
The next letter is ו called Vav and is used not as a "V" but as the vowels U or O. In this case, it's pronounced as a "u" or "oo" sound.
The next letter is כ called Kaf, pronounced like a "K." Sometimes written/pronounced "Q."
The last letter is ה called He, pronounced like an H.
So another valid spelling would be HNVKH, or ChNVKH, ChNVQH for scrabble extra points when you run out of vowels. If you can find "no" on the board, chanooqah should get you mad points, nu, with the +50.
Even the "spelling" changes in Hebrew: חֲנֻכָּה drops vav and adds kubutz and is the way it is written with niqqud (nekudot, "vowels"), whereas the sound for "u" is "always" written with vav in modern Israeli Hebrew when not using niqqud/nekudot.
The consensus, therefore, is not a consensus for a good reason. If my third grade teacher had explained that Ḥanukah was a (foreign/not English) word and changes spelling because it doesn't use a Latin alphabet, I would have not corrected her when she added it to a holiday spelling exam and wrote it inconsistently on the answer key from the study materials. My correction reduced her to tears when she realized her inconsistency - and being too smart for one's own good has never been to my benefit.
But it's a great way to learn that some things which are taught as hard rules aren't always so, and "correct" is (sometimes/frequently) subjective. When someone reacts negatively to how a foreign loan word is spelled, there's almost always another reason why they are angry besides the minor etiquette violation.
If you want to respect them but don't want to get into the politics, you can always say
that is, "Happy Holiday" - that's what Jews say to each other on Ḥanukah. Of course, you'll probably misspell that, too. And, it will tick off the "it's pronounced Christmas" fundamentalists.
More questions on Hanukkah: