This has been discussed in some depth here:
tl;dr: Cookie use in standard Discourse is either non-user-specific or or falls under the ‘legitimate Interests’ basis of data processing and storage, rather than consent. If you’re using third-party services, such as analytics or ad-based services, you may need to obtain consent. In the topic I linked to, there’s some examples of using purpose-built services to obtain consent for cookie use.
To your specific point about notices, you can provide a statement about your cookie use in your privacy policy, in a globally pinned topic and / or in a banner.