once exposed to air, hiv becomes inactive and unable to infect. if, the sex worker didn't wash her hands, (highly doubtful) any residual ejaculate would not be able to infect. transmission takes place INSIDE the body...when a penis is inside a vagina / anus...not through hand jobs.
Are you asking about HIV or STDs in general?If you are concerned about contracting HIV from a hand job well you don't need to worry,it's zero risk.