Oral sex is considered a theorectical or low risk activity for HIV transmission. Factors that make HIV transmission through oral sex  more likely would be an infection present in the giver’s throat. This could be an STI  like herpes or syphilis or a bacterial infection like strep throat. Any open actively bleeding areas in the mouth increase the risk of HIV transmission if exposed to HIV in semen. in general we do not see HIV commonly passed this way. For more information on the chances see https://smartsexresource.com/sites/default/files/Oral-Sex-Table-v3.png