Good evening ! after partner ejaculates on skin is a way to get pregnant,if we put the sperm in a syringe and inject it in vagina ? the sperm cells and still viable on skin ?

Sperms can survive (viable) in wet semen for a while, at least 20-30 minutes, regardless of on human skin or inside a syringe so pregnancy is possible but the chance is much lower compared with intravaginal ejaculation.

Sperm will die quickly when they are exposed to air drying. In medicine we never say never but the chances of a pregnancy occurring after the actions described is not zero but unlikely.