Can you get pregnant if you give a guy a blowjob and he cums in your mouth?

No. No, you can only get pregnant if the sperm are in your uterus and your ovaries have released an egg. You cannot get pregnant by swallowing semen, or even just having it in your mouth.
Unlikely. Sperm need to get into your uterus and then inseminate an egg. Therefore, unless the sperm makes its way from your mouth to your uterus you won't get pregnant.