I agree with all of the above.
Knees don't have anything to do with STDs.
Knee..... none at all.
Unprotected BJ? A small chance of Chlamydia, gono, HSV and Syphilis but these are relatively rare and does not warrant testing after a single exposure unless....
1) Symptoms
2) Piece of mind
3) You know the partner had something.
Saliva is very good at destroying bacteria and viruses.
unprotected oral gives you a small chance of bacteria, and that can be diagnosed with a swab and easily treated with antibiotics
dont do unprotected oral if you will be concerned
no way no how
It's all the feeling of guilt, man.