ou je peux en trouver

So in lesson 5.2, he asks "where he can find them" (the slippers).

If it was just one thing, I would think he would ask: "Savez vous ou je peux le trouver?"
So here why doesn't he say,  "Savez vous ou je peux les trouver?"

Thanks!

Good catch. Yes, technically, «Savez-vous où je peux en trouver  » should have been translated as "Do you know where I can find some (of them)?". (He doesn't have a particular pair that he's looking for. He's just looking for a store that sells something in the "genre" of slippers.)

If he misplaced a pair of slippers and is looking for them, then yes, he would ask for «Savez-vous où je peux les trouver ?» (Where can I find them?)

Also, please note the trait d'union on the inversion, it's not optional.