What is p1k1B

I am not sure how to p1k1B (p1,k1 through back of loop) into yfwd, yrn on previous row

There was a yarn over (yfwd, yrn round the needle) on the previous row. When you come to that yarn over in the current row, the instructions are to p1, k1through the back loop into that large stitch formed by the yarn over. Basically you’ll purl one without dropping the stitch off the left needle and then knit one through the back loop into the same stitch. You can see the ktbl here.

You can expect to see a hole where the yo is, that’s not a mistake. I might be mistaken - someone will let us know if I am!

Sounds like a double yo (yf, yrn) on the previous row and you work a p1 into the first loop and a k1 tbl on the second loop. Though that will close up the hole somewhat - you might see what it looks like if you just knit into the front leg on the second loop.