The most common type of Chinese name uses one character or syllable for the family name and two characters or syllables for the given name. E.g. MAO Zedong, ZHOU Enlai and XI Jinping. If this applied to all Chinese names, it would be easy to figure out which part is the family name and which part is the given name.
However, names consisting of one character / syllable for the family name and one character / syllable for the given name also exist, e.g. GONG Li, ZHU De, LI Ming and MA Yan. In this case, you need to know the most common Chinese family names that use just one character (e.g. Ma / 马). (This can be done more reliably in Chinese characters than in transcriptions.)
Finally, Chinese family names that consist of two characters also exist, for example OUYANG Yuqian and SZETO Kam-Yuen.
So if you want to be certain, you need to ask. Or you can hope that they wrote their family name in uppercase, as I have done in the above examples. (Or learn Chinese in order to learn to recognise common names...)