Gauge is whatever - it’s very stretchy.
This cowl fits snugly round your neck, and has a foldover section knitted flat.
You will need approximately 70 - 75gm of fingering weight yarn, the softer the better as it will be against your skin. You’ll also need a button approx 1” diameter for accent.

NB:
I’m making this again in a soft sock yarn, and the gauge is much floppier. I think perhaps the original yarn was more like a sport than a fingering (we call it 4 ply but I think if it were wpi it would have made sportweight). I’d suggest going down a needle size or 2, if only for the inside part (the part that’s knit on the smaller needles).