In my opinion this means "slip 11 (eleven) stitches as if to purl" . Slipping a stitch as if to purl simply means inserting the right hand needle from the point towards the knitting, as you would if you were purling the stitch.
Do you have a picture of the scarf?
Thank you. The pattern was with the yarn and I tried
slipping 11 stitchs. That did not work. Will look for another
pattern and I appreciate you trying to help