Although challah can be eaten anytime, it's traditionally eaten during Shabbat, the Jewish Sabbath. Please note that if you ever see a recipe for challah that calls for milk, butter, or any dairy ingredients, it's not a true challah recipe. Because challah is eaten during Shabbat, when meat is normally eaten, it must be pareve (not containing and dairy or meat or byproducts.).
Some Jews eat kosher food everyday of their lives. Some only sometimes, some never.
Observant Jews only eat kosher food - but Jewish cuisine food is popular among many non-Jews too, especially in the USA, so people who aren't Jewish might eat it on occasions too.
Religiously observant Jews will only eat kosher food. Less observant Jews will often eat kosher food on certain holidays.
Kosher foods.
They do if they're Jewish. Not if they aren't.
if it's kosher
That depends on whether you're Jewish. Pork is not kosher, so if you're Jewish it's not kosher to eat it. But if you're not Jewish then it is kosher for you to eat anything you like, so long as it didn't come from an animal that was still alive. There are some traditional Chinese dishes that are not kosher even for non-Jews, because the animal is eaten alive, but pork isn't one of them.
You may be thinking of kosher. If so it's what a Jewish person can eat. (meaning if it's not kosher, they can't eat it)
Liver
No, moose isn' kosher.
They eat any kind of meat except for pork. However, it MUST be kosher.
Foods that Jewish people cannot eat are known as 'non-kosher'.
Jewish Germans eat kosher food. Like in other countries though, many products that are sold in grocery markets have kosher certification.
They eat kosher versions of Russian foods.
People of the Jewish religion eat 'kosher" (meaning fit) food because that is the way they were commanded by God in the Tanach.