I doubled this yarn and used a size 11 needle...however, I think it can be done in any size and weight of yarn. Just do a swatch for the size you would like and go for it. No gauge. The infinity pictured is 24" x 8", the scarf would be double the length to 48".
K2tog: knit two together
YO: yarn over
WYIF: with yarn in front
For scarf: Cast on 30
For Infinity: cast on 30 stitches with a provisional cast on in a scrap yarn.
Row 1 (set up row): *k1, yo; repeat from * to end