My husband grew up on a remote ranch in Mexico without electricity, so I hear you on having a spouse who doesn't know what stocks are.
But he's learning. I talk about it all the time, in a casual fun way, and he's getting it. Honestly, it's a lot like his cattle thing he does on the side. He bought a cow from a friend. The cow lives on free-range land within a larger herd. So it get pregnant. Then that baby got pregnant, and on and on, and now we have about 11 cows.
It's likely you're wife has some experience with this type of investing? With the idea that you don't want to just eat all your cows right now, but rather let them grow into more cows. Or beans, or corn, or whatever?
Anyway, even if she doesn't, I'd stay away from handing out books, unless she asks, or maybe if she really likes reading (my spouse doesn't).
But what I do, is log-in, and show him the graphs on Vanguard. Look! We made $1000 in interest last year! Awesome! Free money!!! Or I'll show him the graph that shows contributions (look, here's how much we put in), and then interest (and here's how much we got for nothing).
He's getting more comfortable with the concept. I didn't make it like a sit-down powerpoint lecture, I just talk about it a lot in a natural way.