Why is it pronounced zing in Cantonese instead of gin? My personal feeling is that the word "ru" contains the word "jing" on the edge of the word "ru jing", "jing", "獍" but (mirror), how can I pronounce "geng" again? What should I do? Can someone please explain?

Correction, it’s ging, not gin. It’s normal for these two words to have different pronunciations, because Cantonese retains many pronunciations of medieval Chinese, and many words are pronounced differently from Mandarin. After all, the word "jing" seems to have sharp and round points, and its pronunciation has been different since ancient times. If you ask someone who studies phonetics, I only have a superficial understanding of this.