Hi Webber - the basic working of a skimmer is like this:
- water is pumped into the skimmer body, and at the same time air is either sucked in (by the same pump pumping the water into the skimmer body), OR by a seperate pump...
- the air then mixes with the water, to create millions upon millions of tiny tiny tiny bubbles...
- these bubbles then flows upwards, towards the top - as the bubbles flow upwards, they grow bigger and bigger, collecting protein's and other crap out of the water.
- the "crap" then accumulates in the top/skimmer cup...
Now - you must try and find out whether your pump is not working correctly, that's connected to the skimmer.
OR, IF the pump is indeed working, the air-pipe might be clogged up - try and blow a breath through the pipe where the air is sucked through - see if you see the bubbles coming out inside of the skimmer body.....
There should be bubbles at least - in your pic, I do not see any bubbles....
IF we can get the bubbles to work correctly, then we can look at sorting the water levels....
Good luck.