You should carry your passport with you at all times in a foreign country.
Schools can only demand to see your passport but should never ask to keep it.
Your passport is the most important document you have to prove your identity in a foreign country. It’s illegal to hold onto someone else’s passport in any part of the world. Only government authorities like the police, courts, or embassies/consulates can hold onto your passport by issuing you a legal receipt for it.
The same applies also to your credentials! Schools will often ask to see the original degree and teaching certificate or ask for it to get it translated/notarized. You should only part with it for the interim period of getting your paperwork done. The originals should then be returned to you and should always stay in your possession.
Some schools practice unethical methods of keeping the originals, so teachers cannot run away or jump to another school during the contract or the following school year. It’s illegal for them to do so!
If in doubt, please consult with an attorney. Ask the school to issue you an official receipt for the passport and original documents. Chances are they won’t be able to issue you anything.
I remember my first teaching year in Turkey, a recruitment agency that got me the job was holding my original degree and teaching certificate and would not return them unless I worked with them for three consecutive years. I struggled and finally got an attorney involved who threatened to file a complaint with the Ministry of Education and Ministry of Labor. My issue was resolved, and it left a strain in our relationship but not many teachers know their rights to fight back and normally cave in to pressure.
Most schools practicing such illegal actions will not fight and return your documents if you threaten them with official complaints or even if you threaten to expose them on social media.