Would it be a sin to go on a page or video go on a video or page (on YouTube,Facebook,etc) That you suspect or know is pornographic if your purpose is to report the material.
Probably. Avoid pornography. Policing the internet is not your job.
To report it I would say no it’s not, but if you’re just looking for an excuse to justify being on it then yes it is.
And if you’re not sure, then let someone else report it and stay away.