How can I convince my wife's son that he should study science at university? He doesn't seem motivated challenge himself and just wants to go to his gf's place all the time.
You're probably too late, you have to foster an interest at a young age.
You can try now, but don't expect it to go well. Do something that looks impressive and is easy to do based on your field of study, e.g. if you're a chemist do an iodine clock, if you're a biologist build a 6ft model DNA helix with him. If you're not in any fields you can use, just get a teenager's chemistry set and do those with him.
Or watch Breaking Bad.
>my wife's son
he got Chad's genes, he doesn't need no science, he'll pimp women and smart manlets like you will raise his offsprings
see if you can get him into engineering, if it fails put him in the air force, chicks dig fighter pilots