I think we're so far from that world that this is more a question of abstract philosophy than political theory. But for what it's worth, I think these are the three most common answers to that question:

1. We reach a state of automated post-scarcity in which we don't need people to work;
2. People work for the sake of personal satisfaction or community recognition or some other non-monetary reward;
3. Goods and services are exchanged in a Gift Economy: people still get rewarded commiserate to their labor, but the exchange isn't mediated through currency.

Personally, I don't think it's something that we need to figure out this decades or next.