Fuel gage...
First, at the gas tank, disconnect the plug, then take a short piece of wire and strip the ends. Jump the two wires going to the gage and see if it works. You'll have to make sure you have power on to the gages for this to work in troubleshooing, whether it's the gage or the sending unit.
You do take loose the clamp on the bottom of that rubber gromment that holds the sending unit to the tank. You'll need about 2 and a half foot clearance to get it out. So, if you can't clear that, you'll have to remove the tank or whatever to get it out. On my boat, I can leave the hoses on, but in your ski, you may not have the slack.
Look at the base of the unit where the hoses come together. There should be markings telling where each hose connects. Check resistance with an ohm meter first before you pull it. It may be the electrical board inside instead of the magnets.