I’d recommend leaving a way to contact you as you’re both behind a NAT.

If they wanted to make it possible to contact them they'd have left a contact link on their profile.

If they didn't, they don't intend to be contacted.

nick_m created his (or her) account in 2018 and only posted 12 comments, all in that year.

Seems you may be out of luck.

To get this information, click on your own user id and edit the URL to use the other person's id.

Or just click on their id if you have something they wrote.

You can't. This is intentionally not possible.