What is the ruling on eating Kosher food?

The principle for the meat slaughtered by ahl al-kitab [people of the Book i.e. Jews and Christians] is permissibility. Based on this, it is permissible for a Muslim to eat from this meat provided it is not certain whether or not the animal was slaughtered in the first place or whether the person who slaughtered it was from among ahl al-kitab.
And God the Almighty knows best.