Help with YOs!

The pattern for a shawl reads: P1, yo, sl1, k2tog… Do I do a knitted YO or a purl YO??
Also, would I slip knit-wise or purl-wise?
Thank you!!

Purl one, bring the yarn over the right needle to the back, slip one purlwise then knit the next 2 sts together. The yarn over won’t use a knit or a purl st, it’s simply putting the yarn to the back over the right needle.