You do not have permission to use this content
Surprisingly, the only terms and conditions that you agree to when signing up is the Privacy Policy which doesn’t deal with copyright.
Therefore, everything posted on Paizo.com is unlicensed to anyone (including Paizo) by the original copyright holder - presumably but not necessarily the OP. If push came to shove, Paizo could argue (probably successfully) that by posting the OP granted an implicit licence for the content of the forum post to be used in the way that forum posts are commonly used. However, that’s them, not you - you have no licence to use the material at all.
Therefore, if you choose to use it it must fall within the fair use (USA), fair dealing (non-USA common law), or the specific provisions of copyright law in other jurisdictions. This does not require attribution.
Attribution may help in supporting a fair use/dealing defence or it may just call the author’s attention to the breach and prompt them to sue.
Its probably best if you ask for explicit permission to do what you want