1.打工 only mean working.It can be used for any type of work. 2.聚会 more close to friends meeting.(each other know each other).集会 is more bigger size meeting,more people join,and they maybe don't know each other. They join because they get similar idea and want to share it. 3.using 赚钱 in writing is better. 4.I cant think any now. But using 去 in writing is better.

1) 打工 it could be used for any type of work (part-time, full-time, temporary job, life-time career, etc.)【but it is often used for people who live in small city or rural area went to a big city to work. 】 他去广州打工了。 2) What is the difference between 聚会 and 集会? 【这个周末公司聚会。 他参加了同学聚会】 【集会：some people get together for special meeting especially for a political idea. 他们打算去政府门口集会，抗议政府的不作为。】 3) How are 挣 and 赚 used differently from one another? I understand that 挣钱 and 赚钱 mean the same but what about in other instances? 【挣钱 you work and get the pay （挣 the character has “扌”alway refers action about hands etc. 他外出打工挣钱养家。 】 【赚钱：(赚 the character has"贝“always refers to money) 卖水果很赚钱。 前几年炒股很赚钱。】 4) I have learned that 上 is often used like 去(to go). For example, 你上哪儿啊？/ 我上厕所。 **Are there any instances where 上 CANNOT replace 去? 【“上”has many different meanings: 1 verb+上 他登上了顶峰。 他累极了， 一闭上眼睛就睡着了。 2 noun+上 桌子上有一本书。】