Which is the recharge line for AC on a 2001 Dodge Ram?

There isn't a single "recharge line" for the AC on a 2001 Dodge Ram (or any vehicle, really). The refrigerant charging process typically involves connecting to both the low-pressure side and high-pressure side of the AC system. You'll need gauges to monitor pressure and properly add refrigerant.

Finding the ports:

The low-pressure port is usually smaller and has a blue cap. The high-pressure port is larger and has a red cap. These are usually located near the compressor or on a drier/accumulator near the firewall. You'll need to consult a repair manual specific to your 2001 Dodge Ram to locate the exact ports. A picture diagram in a repair manual or online is extremely helpful.

WARNING: Automotive AC systems use refrigerant under high pressure. Improper handling can cause serious injury or death. It's strongly recommended that you take your vehicle to a qualified mechanic for AC service. Adding refrigerant without the proper equipment and knowledge can damage your system and void any warranty.