In world war 2 were people forced to admit their jewish? Or they killed people they thought were jewish?

Well you know the whole penis mutilation thing kind of makes them stand out like a sore thumb. Or a sore penis.

Nobody was killed for being Jewish. International Jewry declared war on National Socialist Germany in 1933, so the Jewish population became self-declared enemies of the state. When Britain declared war on Germany in 1939, the Jews were placed in forced labour camps. About 200,000 of these Jews died late in the war due to a Typhus epidemic.

Everyone registered their religion, it was even on birth certificates at that time,so it was easy when the nazis started to arrest jews, they knew where to look!

The Nazis used records to identify who was Jewish (prior to the war the Nazis compiled detailed records using early computer equipment). In occupied lands where they weren't such records, they spoke to neighbors and the local government. Still, there were some people who were able to hide using assumed non-Jewish identities.

They knew already. There was no "admission".

It never had anything to do with admission;never were they challenged to admit it. Also, it had nothing to do with what religion they professed. Many people mistakenly believe that changing to Christianity was the issue and could have saved them;it was not that either. It had to do with ethnic Jewishness, regardless of religious beliefs or the lack thereof. Years prior to the holocaust, IBM helped the Nazis develop special technology to identify persons of Jewish descent, not only in Germany but also in the countries that the Nazis anticipated conquering, and made a special cardboard IBM card to go into a computer so that they could be tracked and identified, even if they moved. That IBM computer is now on display in the St Petersburg. Florida Holocaust Museum. An interesting side note to the subject is that "Meschlings" or persons of one-quarter Jewish descent were allowed to serve in the German army, although their pure Jewish grandparents were exterminated, and the Nazi High Command actually sent them letters to that effect when their grandparents were gassed, and showed its banality by being mystified that thousands of young privates went in tears to their sergeants after receiving such notifications: This is well documented in a book called "Hitler's Jewish Soldiers" by Bryan Riggs.

Both.

When asked for their papers many countries had religion listed on them.

If you are talking about Germany then no, years before census had been done so the Germans knew who was of Jewish faith and who wasn't

Suspicion of being Jewish was enough.

Neighbors informed on other neighbors, the practice of the Jewish faith was forbidden, and yes, even non-Jews who were reported were killed.