Use a GoPro on a stick. Or build a fancy MALP and charge it to the project.
In this age, everyone has a camera handy. If the issue arose spontaneously, someone could use a “selfie stick” or improvise a handle for a phone used as a probe.
For an intentional effort well planned, obtain a ruggedized and shielded camera, and even rig control lines that pass through the wormhole without losing the signal: acoustic signals for low res images (off the shelf!), and mechanical control lines like for bicycle levers. Ideally, a superconductive shield can make a cable that passes through, so some very expensive co-ax will give you full high-definition feed. Otherwise, view low-res images live using other non-electrical (or just very noisy) means, and retrieve the camera to view the HD recordings.
As for figuring out whether it’s safe and what to wear, take a page from the spaceprobe book. We have spectrometers and fancy sensors, even something approaching the StarTrek tricorder now, on Mars.
Now you don’t want to drop your million-dollar gadget on Venus, to use a real-world example. So start with the selfie stick! A cheap mobile device platform has camera, thermometer, barometer, magnetometer, etc. If you pull the stick back and the device has been melted, you’re only out $40. Include some passive samples of materials; perhaps in the form of a case, and you’ll see if there’s acid or something that would bother your expensive instruments. Based on that result, design a protective enclosure to suit the environment.
Actually, use two cameras, on both tests. Have a simple, durable mobile camera lens built into the stick, about half way back so it doesn’t come very far from the portal, and it’s streamlined with the stick and doesn’t look like a separate box. That way if the stick comes back without the probe, you can see what took it via the backup camera. Used with the main (expensive) probe, this serves as a nav-cam for monitoring how the probe is positioned and if anything is around it.