Cunnilingus is lower risk than other sexual activities, but there is still a risk.
You can get syphilis if your partner has a sore. You can possibly get gonorrhea or chlamydia in your throat, though it's not as likely as performing oral on a penis, since the penis will enter the throat.
You could get oral HPV. This raises the question of transmission and oral cancers. Oral cancers are rare, but definitely possible, and if you are performing oral on other partners, you could transmit it. HPV is incredibly common, and you can get this from anyone, not just a CSW. Guardasil-9 will reduce your risk greatly, but not totally. It protects against the most common high risk strains, but not all of them.
You won't get HIV, any of the hepatitis viruses or oral herpes from performing oral.
Some CSWs won't allow oral without a barrier, and this is smart. They need to protect themselves from their clients.