I was always taught growing up that "next" Monday is the one after "this" Monday which is the first Monday you will encounter moving into the future.

I was surprised as an adult to discover that this is not universally held. Since it's pretty obviously ambiguous, I would expect my voice assistant to ask for clarification on which one I meant, and maybe learn from that if it's the kind of assistant which keeps user profile data (which is probably all of them).