Any decent synthetic silicone lube should take care of it. Personally, I would recommend MechLube, but it's really user preference.
Fyi though, when I first got my Ducky Shine II it was squeaky on the space bar. It wasn't everytime, but it was when I would push it rather rapidly during typing and stuff.
However, it doesn't do that now. I think it's not that good to lube up unless you're really having a problem because it introduces more particles to be stuck there and eventually turn like sandpaper. Plastic and metal rub lightly to form dry lubricant (basically powdered plastic). That seemed to do the trick. If you do use lube, make sure to keep your keyboard free of foreign debris.