2002 Kia Sportage leak

It's almost certainly leaking from the heater core. Generally the heater core, or its connections, are visible on the engine side of the firewall. You will see two rubber hoses within a few inches of each other. These are the input and output ports of the core which is essentially a mini radiator that the heater blows air through. The hot coolant provides the heat source.

What happens is that over time the core can corrode and develop a pinhole or it can just crack from age and getting bounced around in your car.

A new one is probably not all that expensive but for most models these days, the core must be replaced from the inside of the vehicle and generally requires taking the dash or most of the dash apart and out of the vehicle. Depending on your skills this may not be a job for a DIY mechanic.