user15223: As I write this question, Ian Nepomniachtchi is leading the ongoing Candidates tournament by a substantial margin. Since it's a winner-takes-all tournament, everyone else needs Nepomniachtchi to lose.
Are the other players allowed to discuss how to achieve this collective goal? For example can they suggest openings to whoever is playing Nepomniachtchi, or discuss whether one should take risks and possibly lose in return for a chance at winning (as Rapport did in his game against Nepomniachtchi )?

user4418: 
Are the other players allowed to discuss how to achieve this collective goal? For example can they suggest openings to whoever is playing Nepomniatchi

While the games are in progress this is strictly forbidden. In between games this is perfectly acceptable. What would not be acceptable would be to pre-arrange quick draws amongst themselves to conserve energy for their fights with Nepo. This would be match fixing. This happened in Soviet times when the Soviets dominated world chess.
The FIDE 2022 Ethics and Disciplinary Code defines the offence of cheating as:

e) Cheating: Any player, or any person assisting a player, who deliberately -
(i) Uses or attempts to use electronic devices or other sources of information or advice during a game;
(ii) Commits a manipulation of a chess competition such as, including but not limited to, result manipulation, sandbagging, match fixing, rating fraud, false identity, falsification or alteration of birth certificates, and deliberate participation in fictitious tournaments and games or any other false information with the purpose of obtaining an unfair advantage for a player or a team.


15223: <p>As I write this question, Ian Nepomniachtchi is leading the ongoing Candidates tournament by a substantial margin. Since it's a winner-takes-all tournament, everyone else needs Nepomniachtchi to lose.</p>
<p>Are the other players allowed to discuss how to achieve this collective goal? For example can they suggest openings to whoever is playing Nepomniachtchi, or discuss whether one should take risks and possibly lose in return for a chance at winning (as Rapport did in his game against Nepomniachtchi )?</p>
 4418: <blockquote>
<p>Are the other players allowed to discuss how to achieve this collective goal? For example can they suggest openings to whoever is playing Nepomniatchi</p>
</blockquote>
<p>While the games are in progress this is strictly forbidden. In between games this is perfectly acceptable. What would not be acceptable would be to pre-arrange quick draws amongst themselves to conserve energy for their fights with Nepo. This would be match fixing. This happened in Soviet times when the Soviets dominated world chess.</p>
<p>The <a href="https://handbook.fide.com/files/handbook/EthicsAndDisciplinaryCode2022.pdf" rel="nofollow noreferrer">FIDE 2022 Ethics and Disciplinary Code</a> defines the offence of cheating as:</p>
<blockquote>
<p>e) <strong>Cheating</strong>: Any player, or any person assisting a player, who deliberately -<br />
(i) Uses or attempts to use electronic devices or other sources of information or advice during a game;<br />
(ii) <strong>Commits a manipulation of a chess competition such as</strong>, including but not limited to, <strong>result manipulation</strong>, sandbagging, <strong>match fixing</strong>, rating fraud, false identity, falsification or alteration of birth certificates, and deliberate participation in fictitious tournaments and games or any other false information with the purpose of obtaining an unfair advantage for a player or a team.</p>
</blockquote>
