Can a girl get pregnant if a boy first touches his penis, have some semen on his hand and then touch a girl's vagina with the same hand?

Depends on variables: If the hand carries sperm to the vagina there is the possibility of a pregnancy. It is muck less likely than with intercourse, and will not occur if the sperm are dried out or otherwise made inactive prior to contact.

Probably not...: But if you want to be sure, i would recommend purchasing and using a home pregnancy test. Good luck!