How do China citizens apply for a Thai tourist visa, E PASS tourist visa?

You took EP to travel to Singapore? I don't know what this means.

Anyway, since you are going to Thailand during your stay in Singapore, the China passport of Thailand is landing visa. There is no need to apply for a Thai visa in advance. You can buy air tickets directly and prepare 1000 baht and passport photos.

If it is a domestic direct flight to Thailand, because Thailand is not on the release list of the border inspection, you can't go directly to Thailand with a white passport, so you need to apply for a Thai visa in advance to fly directly from China to Thailand. In Singapore, there is no such trouble. Just buy a plane ticket.