Adjective declension, feminine locative singular → -ej.
Swój declines like an adjective, apart from the shortened form in masculine nominative singular.
You can say robotnik for a woman if you are reffering it as a work station. "Ona jest robotnikiem" - "she is a worker" If you want to underline the fact that she does physical, often dirty work, saying robotnica would be more adequate. Although it's worth noting Poles usually say "robotnica" in bee context :P. If you ever are in trouble, google image a word and see what are they differing from eah other.
"robotnik" is masculine. Polish cannot use 3rd person plural 'ich' as English can do with the gender-hiding 'their'.
Also, we have no way of knowing if a person using 'their' does it consciously, or makes a big grammar mistake compared to what they (sic!) actually wanted to write. Most users aren't native English speakers, and they can make all kinds of mistakes.
So, to reinforce the 'masculinity' of the word 'robotnik', we can only accept 'his'. I know some people will disagree, but generally the reports asking for it are a lot less common than I would expect.
In English "employee" and "worker" are interchangeable but this is not the case in Polish? Robotnik is more like what we in English consider a manual laborer? Example: ship yard worker, lawn and yard maintenance, movers/ removalist? I ask because I entered: " The employee is talking about his job." and it was rejected.
Both are correct and accepted, actually. But only one makes sense in most contexts.
Any form of "swój" refers to the subject of the sentence. Therefore "Robotnik mówi o swojej pracy" means that he is talking about his own job. "jego" may be the literal translation of "his", but in fact it suggests that this is some other 'he'. So in "Robotnik mówi o jego pracy", the worker talks about someone else's job. Joe is talking about George's job. "his" doesn't have this distinction (apart from using 'his own', but that's technically something a bit different and would be translated as "swojej własnej"), so both translations are correct.