Are those who are not baptized ever obligated to attend Mass every Sunday?
If someone is in RCIA I encourage them to live a Catholic way of life as much as possible. That includes things like going to Mass, praying, participating in various ways in the parish, following moral teachings, etc. It won’t happen all at once, but by the time they are ready for baptism being Catholic should be part of their being.
I think the answer would be that canon law does not oblige the unbaptized to attend mass, but all the unbaptized are morally obligated to become baptized, after which they are obliged to attend mass every Sunday.