Where on the internet would you discuss a specific case of a potential exploitation of a minor within the adult industry?

In the US, you can report child exploitation to the FBI. Outside the US, you might look to see if your country has a similar internet task force.

The specifics are not something that should be discussed publicly, out of respect to the child.

It's not a thing you discuss, it's a thing you report. If you aren't sure, report what you do know so they can open an investigation.

You should maybe indicate if you're critical of this exploitation or in favor. If it's the latter it would be easier for the mods. And if it's the former you would lessen the inherent yuckiness people feel when reading this.

This is understandably vague. Other people have mentioned the US FBI, but there's also the NCMEC and IWF. If this is a professional-looking work, you may want to engage the studio's compliance office. There are a number of very young-looking performers that were confirmed legal adults, so it might be a false alarm.

If you found something on PornHub or similar (possibly including Facebook), they usually have a 'Report' link. If you claim it contains minors, they will likely handle reports to the authorities automatically.

If you are looking to discuss whether a work contains a minor, outside of an abstract like the Traci Lords videos, I would recommend against it. Get the compliance records from the studio, or report it to authorities.