In a true communist society (which has never existed above the commune level), individuals would own nothing. Society would own everything. There would be no need for currency.
From each according to ability. Each individual would be assigned tasks and expected to complete them. It's much how salaried personnel work. Each person would be responsible to that person's supervisor for getting work. That supervisor would in turn be responsible for the production of the team to the supervisor's supervisor. So on and so forth until some supervisor (who might be called a minister or cabinet secretary or something else) is responsible to society.
You wouldn't have to prove that you worked. Everyone works. If you didn't work, your supervisor would come and tell you to work. What happens if you refuse? Theory remains vague on that point, which is part of why we've never had a real communist society.
To each according to need. So you would go to a supplier and demonstrate a need. Again, how that works is a bit undefined. But someone, would determine for your individual case if you needed e.g. a package of toilet paper. Using too much? Perhaps they might ask you to consult a doctor for diagnosis.
Again, if you work as e.g. a cable technician, this process will be familiar. You go to the supply clerk and ask for cable fasteners. The supply clerk looks on the computer and sees if you are on schedule. If you are using too many, the supply clerk may refer you to someone else. You can then explain why you need more than most people.
This kind of stuff works at the corporate level because if a company does it badly, another company can do it better and therefore more cheaply. We use money to give people control over that. My job pays me money which I then pay to companies so that they can pay their employees. If one company is inefficient, they raise their prices. I switch to a different company. The first company goes out of business (assuming most others switch too). The surviving companies expand, hiring many of the workers of the bankrupt company.
Communism (and government in general) has been less successful about coming up with a replacement for that process. National democracy doesn't work for things that are inputs to other products. Too many people will know nothing about the issue. You need something controlled more locally to the industry involved. But what about things that are end products? They are consumed nationally even if produced locally. How to balance the national consumer interest with the local production interest?
The free market response is to allow each individual to control their own consumption and production. The combined decisions of everyone form the market. Communism has yet to develop a practical replacement that works.
The result is that in practice, every communist government (e.g. the Soviet Union) has still had currency. So they haven't been true communist societies as envisioned by Engels, et. al.
Perhaps the answer is that Engels was wrong in how to achieve his goals. Perhaps the true system that meets the goals of communism is the one used by Denmark. Denmark has money and private property, but it also has a substantial welfare state. And many services are provided out of tax money rather than through purely private transactions. Or as hybrids. Individual transactions subsidized by the government. It's not clear that Engels would agree though. And Denmark does not think of itself as a communist system.
Perhaps the real answer is that the theoretical model of communism is impossible to implement. A new model would have to be proposed. Since it hasn't yet, we can't really say if it would have currency or not.
In my opinion, Denmark is closer to meeting the goals of communism than any actual communist state. I.e. the poorest person in Denmark enjoys more access to resources than the average person in the Soviet Union did. So if you throw out how Engels, Marx, et. al. thought that communism would work and instead set a variety of measures, Denmark's system outperforms any actual implementations of communism. So Denmark may better represent the "victory of the proletariat" than any communist country.
