the possessive pronoun of someone/somebody is either "his/her or their" so instead of saying: ..where someone working in his/her job, you can say for short: someone working in their job. it's then obvious that "their" can be used as a gender-neutral possessive pronoun; that is when the gender of the subject is unknown or could be male or female. consider this: i saw someone trying to open the car's door, and there was a torch in their hand. the speaker can not tell whether the thief was male or female that's why he/she uses "their". likewise, "they" can be used as a gender-neutral subject pronoun. consider this: i saw someone trying to steal the car, and they had a torch in their hand.

their shows ownership of a following object by a previously mentioned subject. The previously mentioned subject is "someone". The following object is "job".