So I looked. The adjuster knob on my skimmer that has water line sticker is just under the water. Not even an inch.How many inches is the waterline? Every skimmer has a max and minimum depth of water it’s designed to run in. If your dial is maxed then the skimmer needs to be in deeper water.
If it’s on a stand, then lower it. Or move it to a deeper compartment. Or the skimmer is not compatible with the sump you have. Or the skimmer is overrated and you don’t have enough bioload to make the skimmer function properly.