YO is also known as - yo, yarn forward, yf, yfwd, yfon (yarn forward over needle), yfrn (yarn forward 'round needle) and others depending on the origin. Why it's written two different ways in one pattern I don't know.
There are hundreds of dishcloth patterns if you'd rather switch.
For the yf, yarn forward, bring the yarn to the front and then over the right needle to the back to do the k2tog. For the yrn, the move is a little different but the effect is the same. Bring the over the needle and then back around to the front so that you're in place for the p2tog. These are as Jan says just different ways of saying yo or yarn around the needle, depending on the designer's preference.
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