"Robotnik" means *manual* worker. E.g. someone fixing roads, or working in a factory.

"Pracownik" is a generic word for "employee". Can be an office worker or an manual worker.

"Robić" basically means "to do". While "pracować" means "to work". As you can notice one is more formal than another.

"Robota" is a less formal word, something closer to a "gig" (however it also means "work" or "job"). You will probably not find it in written texts. In writing "praca" (work) sounds more formal.

As a bonus, if you are a (manual) worker who complains and makes some not subtle digs about your job, you can say that you "have to go to your kołchoz tomorrow" ( https://en.wikipedia.org/wiki/Kolkhoz ). As the communist slogan said "work is your second home" after all :)

On a side note, do Czechs really like the polish word "pomidorek"? (Little tomato)