This is a simple V stitch with the yarn held double to make this all squishy. To get the same results as pictured you can either use
two strands held together or with a bulky weight yarn.

Gauge
-Doesn’t really matter for this project.
-Changes in hook size and yarn weight will have different effects. For a loftier effect, use a bigger hook. If you use a single strand of worsted weight your scarf will be skinnier and need more rows for desired length.