"The worker talks about his job."
Translation:Robotnik mówi o swojej pracy.
"Robotnik mówi o jego pracy" "Robotnik mówi o swojej pracy"
What's the difference? Is there one more often used than the other?
Swój is used when the possesive pronoun refers to the subject of the sentence (and not to some different person).
"Robotnik mówi o swojej pracy (=his own job).
Robotnik lubi chwalić swojego syna. Teraz opowiada nam o jego pracy. (=the son's job).
There may be some differences if you make up some specific context but basically that's all you need to remember. PS For those who know Swedish/Danish/Norwegian it works exactly the same as sit(t)/sin.
You may want to check out this post. I couldn't find any discussion about this particular topic there but maybe you'll find some other helpful explanations.
Locative. When "o" means "about" = "on the topic of" (as we realized that it doesn't work for example for 'to worry about'), it takes Locative.