There's only 5 fittings, in and out of the condensor behind the front grille, in and out of the evaporator at the drier, and the manifold at the compressor. The high side quick connect on the manifold is prone to leaking, mine does, but also the low side could leak and there's another schrader fitting on the drier. Apart from that some trucks have had issues where battery acid leaked onto the line that runs past the battery from the condenser to the drier and corroded it. AS I already mentioned oil will come out where it's leaking. I can't actually see any oil on mine, but the compressor leaks in the center. You could have a leak in the evaporator coil or condenser coil but it's unlikely. My money is on the compressor
Edit: Could also be leaking from the high and low pressure switches. The high is on the drier, schrader valve I mentioned, and the low is on the back of the compressor.