Question: how to do a yarn over on a purl row?
Answer: To make a yarn over (abbreviated yo) between 2 purl stitches (which you'd encounter in a pattern as p1, yo, p1), just do the following: Purl the first stitch. Wrap the yarn around the RH needle front to back to front so that it ends up in purl position again. Purl the next stitch (see the following figure.)