If you double stranded to make the shawl then you will do the same for the edging. It is the continuation of the pattern only it is crocheted instead of knitted.
>>The best place to join is at the end of a row but you don't have that option. You can join the yarn wherever necessary with whatever joining method you want(knot,oh no, Russian). Leave enough to weave the ends into the knitting or you can hid it in the crochet work that you are doing. EZ said do three or four stitches with the new yarn and the old. The hiding method is your choice. I know the edging will go great with the rest of the shawl.:cheering: