Check the hot and cold fittings on top of the heater for leaks. Likewise the drain valve at the base. If the T&P drain line ends at the pan, feel inside it to see if it is wet. All of these things can potentially be fixed.
If it’s none of those, however, there is a good chance it is the water heater and there is nothing you can do but replace it.
You don’t say if it is gas or electric. If gas, you can look in the combustion chamber for signs of water. If electric, the same with the element ports, after turning off the power.
You can feel all around the jacket. If one spot is hotter than another, there is probably a leak there.
If you decide it is a goner, read the appropriate sections of The Basics before going out and buying a new heater.