The risk of HIV through oral sex is negligible. You can test for HIV 28 days after the exposure if you go for a duo combo ag/ab test. If you go for an antibody test, it will be accurate 90 days after the exposure.
Oral sex exposes you specially to syphilis, gonorrhea and herpes. You can also get chlamydia theoretically, but the risk is so low and there are experts that say is not possible to get it this way.
You can test:
-For gonorrhea and chlamydia, 3 weeks after the exposure.
-For syphilis 6 weeks after the exposure, and if you get it negative, it would be interesting to re-test again 3 months after the exposure, as there are people that take longer to show a positive result.
-3 months after the exposure you can test for herpes.