I don't trust Midas blennies a whole lot - they can be really nippy and sly. However, newly acquired yellow wrasses are really prone to a disease called Uronema. There isn't really any treatment for that, and this fish isn't showing classic signs of that disease, so I would circle back to possible aggression from the Midas blenny.
Jay knows this one. . . . Rather than keep an eye on Midas or others who will be on their best behavior when youre watching tank, Grab your cell phone and place on video mode. Record for about an hour and drop a little food and walk away. Review video later and see if you see any aggression which happens at feeding and via boredom.
You may never directly see the blenny do anything - looking at your wrasse, it has only a couple of lesions that took a split second to occur - odds are, you'll never see it happen. That said, the hole in the dorsal fin is NOT a common location for one fish to bite another one.
