If guys penis touches a girls vagina but not in vagina or pre cum goes on vagina but not in vagina, does that leave the guys DNA/gene on/in the girl?

Curious wording. Yes, if your semen got on a girls genitals it would leave DNA behind. If there were a reason for someone to test the area for that DNA they could find it. If you had contact with a girls genitals without her consent or if she was underage, this would be the "smoking gun" that puts you in jail for assault.
Sure, but... People who touch one another can leave traces of DNA on one another. But the traces may be so small that they are not detectable. If the DNA is not detectable, then one might say the DNA was not there... but none of this matters in normal everyday life.