It's hard to explain for me but gonna try my best. Let me explain it by giving an example below :) ex1) 영어 (잘 하시는거 보면) 완전 부러워요! I'm so jealous of you (speaking/to speak) English (well)! ex2) Andy가 영어하(는거 보면) 외국에서 살다 온 것이 틀림없을거야. Andy must have been to aboard (as) he speaks English well. Each of the examples are pretty commonly used in Korean. 잘 means well or good so you could see that 잘 sticks to 하시는거 보면 when it comes to in korean however it's divided into two parts in English. So let's focus on -는거 보면. -는거 보면 in parenthesis basically could refer to like a gerund or infinitives but I'd rather say it performs a role which bridges between two sentences like as in English. It's is kinda hard to explain but hope you get the idea overall.

잘 하시는거 보면... 한국어를 잘 하시는 거 보면.... I know that your Korean is very good. so...