Variable. A Chinese emperor always had multiple names. Most common, I think, is of course huangdi (皇帝) which is just the title of the reigning monarch. Emperors who abdicated maintained the title of 太上皇. When referencing the emperor himself, saying the equivalent of “Her Majesty Queen Elizabeth titles titles” would be a grave sin, due to the so-called “name taboo”. You instead would simply say “His Imperial Majesty, the Emperor” or 陛下 for “Your Imperial Majesty”. There was no need to add a whole bunch of other titles since by tradition and by definition the Emperor of China was the son of heaven, appointed to be emperor of all peoples thus making regional titles redundant. I reckon this is also partly due to China’s absolute dominance in Asia. Japan, Korea and Vietnam all recognized the title of 皇帝 as exclusive to the Chinese monarch, and so there was no need to say “His Imperial Majesty, Emperor of China, blah blah”. 皇帝 was absolute in its connotation. In Korea especially, the title of the reigning monarch was even changed to show this subservience, as Joseon regents were titled as grand kings or 太王, not emperor (hence Kingdom of Korea). Of course there will be some meaning lost in translation but that’s the general jist.

When the emperor lived, he could carry one or numerous era titles (like the Yongle 永乐 era ruled by the Yongle emperor 永乐帝). I’m not actually sure if referring to the emperor by way of his era name was proper, but nowadays this convention is most often used for Ming and Qing emperors in Western convention. Many Chinese sources still use temple names, so...

Speaking of temple names and posthumous names, these are probably the most formal of an emperor’s titles, given upon death. Temple names were usually short, no more than a few characters and there was always a formal convention for assigning them. The founder of a new dynasty was always 太祖 or 高祖, “Grand” or “Great” progenitor, and founders of new branches also used the word 祖 in their temple names. All other emperors used 宗 or “ancestor”. The second emperor was almost always 太宗, or “Grand ancestor”. Posthumous names could be... messy. Just go look one up from the Ming dynasty. But these names always reflected upon the rule of the emperor, not the lands they ruled. So in that sense, Imperial titles in China also differed from European ones in their focus, I suppose.