China passport holders and Indonesian visa holders, who are in Indonesia, want to travel to Singapore for two days and then return to Indonesia. Can I get visa-free or landing visa?

No, you must get a visa. You can do it at the Singapore Embassy in Indonesia in Jakarta.

Also, if you leave Indonesia, no matter where you go and how long it takes, your Indonesian visa will be invalid and you can't return. If your Indonesian visa is for work, you can apply for one-time or multiple entry permits at the Immigration Bureau, so that the visa will not expire. If it is a tourist visa, it doesn't matter. Just go back to Indonesia and apply for a visa on arrival.