This right here. If you have to ask this question before you trace a pipe back to it's source and figure it out for yourself, you should not be fucking with gas lines.
Follow the pipe and see what it connects to. If it connects to another pipe that is attached to a faucet it's water. If it connects to another pipe that attaches to your furnace it's gas
Yeah it's not dangerous to just open it for a second to smell. The handle looks to be blue though, so i'd wager it's more probable to be water and keep a bucket under it.
its like kinda open on the bottom so not all the way plugged? kinda the main reason its confused me tbh ive never seen an attachment like it in my life
So that's an NPT plug on the bottom. Hold the ring above the plug with one wrench and use another on the plug to unscrew it a bit. It's painted over so it'll be tough, though if you squeeze the two wrenches together it should come.
Just unscrew it a bit, and if the upper wrench is moving, stop and make sure you aren't messing up the valve since if that ring comes off the bottom of the valve, you'll have a hell of a time because the valve will drop apart.
If you crack the valve and smell gas, you have gas to that valve. Unless there's another valve or that line is cut off, I would bet money that is gas. You will now need an NPT to flare fitting to put where that plug is, and an appropriate length flexible extension pipe from the dryer to the flare fitting. These are usually a yellow extension that you get at the hardware store. Get one long enough to be able to pull the dry our a bit and move it around, but not overly long. Use some gasline teflon tape (yellow again) or gas pipe dope to put the NPT adapter in, but don't use anything on the flare fitting connections at the adapter and the dryer.
When you have everything hooked up, use soapy water and turn on the valve. If you see any bubbles at any of the connections, turn it off and tighten. It shouldn't take all that much force to tighten a flare fitting so don't go overboard.
If any of this confuses you, stop, watch some youtube videos, and if you're still uncertain, hire a professional. Most plumbers can do minor gas fitting like this for you, you don't need a gas installer.
It's a gas line. It has a plug. Remove the plug and install the flex line. If you don't have a line you have to buy the installation kit for your specific dryer.