Can a girl get pregnant by touching a doorknob with semen on it and then touch her vagina after?

The sperm in semen become inactive/die soon after they are place in such a setting. They are not tolerant to the environment outside the sites of production or the moist inner female genitalia. It is a good practice to consider door knobs a rich site for germs and washing or sanitizing you hands frequently is always a good idea (& kills sperm).

SEMEN ON A DOORKNOB IS LIKE A FISH OUT OF WATER,THEY BOTH DIE BECAUSE OF AN UNFRIENDLY ENVIRONMENT.A DOOR KNOB IS NOT A VAGINA SO DON'T WORRY. ALWAYS WASH HANDS BEFORE AND AFTER SEX.