How do I knit the scarf like this? (Picture)?

Because the scarf is knit in stockinette stitch, it will curl for you. That is the way it is. To prevent this, you knit the edge stitches (border stitches) with some other stitch to control the curl. There are a number of different stitches you can use. Honestly, it is difficult to see from this photo what stitch was used, but it appears to be a 1/1 rib, with slipped stitches. With machine knitting, they can do many things that are more difficult for us by hand. I've not done this one myself. I tend to use garter stitch on 2 or 3 stitches, or even seed stitch, or simple 1/1 rib. They all work very well in controlling the curl of stockinette stitch. Try these on a sample and see which one you like best. It doesn't have to be exactly the same as the photo to work.