Hey @AlkaFire,
Ice Fang is an egg move for Luxray, so if you want to teach it that move, you'll need to visit one of the daycare centers.
There's one daycare per region, so you can visit all these possible locations to get that move for your Luxray.
If you haven't unlocked the daycare centers yet, you can check out the Egg Move Guide. Keep in mind that each egg move will cost you $15,000.
Hope this helps. Have a great day.
Armin