There absolutely is Kosher food available in Terminal A, center pod (gates A20 - A28)
Note: These are items prepared under the Star K and include great wraps, sandwiches and salads. Food is excellent but generally not available on Sunday or the day after any Yom Tov.

Place: The Grove.

I have checked and not found this at any other location in Newark. So, if you are travelling out of terminal C, for example and need to get to this location, there is a shuttle bus after clearing security.