So I will do my best to answer your questions, but from the start, let me say that it will be a lot of guessing because her pap smear only tests her cervix. We have no idea if she has it in her mouth. We also don't know if your friend was infectious a month ago.
So your questions -
1. What is the likelihood of contracting HPV from a single oral encounter vs say penetrative sex? I found studies that suggested in 6 months of vaginal sex, with an average of 4 sessions a week, only 20% of people managed to pass HPV on to their partner. I've read that oral chance is even lower, can anyone add to this data?
We don't have stats on this, and I'm not even sure about the accuracy of your PIV stats. There is no accurate way to test men, and if they are only going by symptoms, that's not a great measurement. Were condoms used?
Generally speaking, oral sex is lower risk for all STDs than vaginal or anal sex. We do know that much.
2. Presumably a smear test only checks for HPV present in the genitals? And HPV via oral sex is only transmissible via oral if present in the mouth?
Yes, a pap only tests the cervix for the presence of HPV, and HPV from oral sex requires the presence of oral HPV.
3. Does having no active oral HPV symptoms also lower the chance of transmission? I know symptomless transmission is possible, but how does it affect chances?
No, most oral HPV is asymptomatic.
4. How does having the HPV vaccine help post possible transmission. Does it help the body clear the infection faster?
There's no real good evidence for this, but it sure doesn't hurt. If you've not had the vaccine, and you are this worried about HPV, you should get it. HPV is incredibly common - it is estimated that upwards of 90% of us will get it at least once in our lifetimes. You may have already had it and not known it.
5. I understand that 90% of people with the high risk strain clear it within 2 years with no health problems. Of the 10% that remains, how likely are these people to contract cancer?
Not likely. In the US, HPV causes 3% of all cancers in women and 2% of all cancers in men. (https://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents/hpv-and-cancer#cancers-caused)
6. I'm reading that 42% of Americans have HPV, but only 7% have oral HPV. I assume this means the chances are much lower of contracting it in this encounter.
Yes, that's accurate.
What are the chances of getting HPV from *receiving* oral? Lower or higher than performing it?
Depends on who you're performing it on. If you only perform it on vaginas, it's lower than if you perform it on men.
Receiving oral is probably lower risk than if you have a vagina than if you have a penis.
This is true for all STDs. Most STDs reside in the throat. The penis enters the throat during oral sex. The vagina doesn't.
7. I'm trying to understand my moral obligations. I want to do right by future partners, but given I can never test to ensure I'm clear what do I do?
Your doctor is an alarmist. You received oral from someone who has genital HPV, and who was kind enough to tell you.
If you are using condoms for vaginal and/or anal sex, I see no reason to mention this. I would recommend getting the vaccine for your own protection, though.
And find a new doctor. I wouldn't want him in charge of my sexual health. It's like he's never had a patient with HPV before.