Can sperm travel through a girls jeans and underwear? no direct contact, penetration

No risk, no worry: Neither sperm nor STD germs can pass through clothing, even if moisture does. Don't worry about it.

Very, very hard: for a little sperm to make it through those barriers. The only way it would be remotely possible is if the clothing barriers were saturated with ejaculate/ pre-ejaculate & pressed up against the introitus. But, the scenario you presented would make pregnancy VERY unlikely.