What language do Singaporeans usually study and work in, and what kind of writing language do they use?

To be exact, 72% are from China, not China.

The official language is English, but Chinese Singaporeans know more or less Chinese (they speak Chinese).

In daily communication, young people prefer English, followed by their mother tongue. However, most Chinese in Singapore immigrated from Fujian in the early days, so most of them are not familiar with Minnan dialect, and the second largest part is Cantonese, who can speak Cantonese.

Many billboards are in pure English, but occasionally they are marked in Chinese. In Chinese publications, it's all in Chinese.

Both subway (MRT) ticket vending machines and bank ATMs have Chinese options.

Even if English is not very good in Singapore, don't worry about not being able to communicate. Just speak simple Chinese to Singaporeans, otherwise they won't understand you very well. The language is the same. Chinese is one of the official languages in Singapore, but the characters are traditional Chinese characters.