When speaking to other British people, I would always naturally pronounce 0 as 'oh'. In a more mixed environment (foreign speakers, speakers of other dialects of English), I would say zero because it is easier to understand and more widely understood. Oh can be misheard but zero cannot. Some speakers of English only recognise 'oh' as a letter. As this is the emergency number of a country where English is not a native language, I'd say one one zero.

more native is to yell "call the police!" or "call the doctor!" instead of playing with numbers

There are several ways people might say this. Even in the US some people say 'nine one one' while others say ' nine eleven.' Possiblities for 110 are: One ten one one oh one one zero eleven zero eleven oh. I'd say the most likely to be used (and least likely to cause confusion) are: one one zero or one one oh

I would say it's pretty interchangeable , but I would personally use 'one one zero' to be clear.

I don’t think it’s standardized. Americans originally said ‘911’ as ‘nine eleven’ so a third option is to say ‘110’ as ‘one ten’. (Now I think ‘nine one one’ is more common. ) By the way, here you use it for any kind of emergency, not simply to access the police. Similarly the spoken version isn’t standardized in other countries and languages. E.g. ‘Un-un-deux’ or ‘cent douze’. Personally I think the best would be to directly anglicize what is said in Chinese but I don’t know what native English speakers living in Taiwan actually do say.