I work in a warehouse setting, and we have exposed metal AC ductwork. The problem is the ductwork gets condensation dripping off it. Can anyone tell me what's the best insulation to fix this problem?

Usually a product called duct wrap works well to control the moisture. It is best applied when the duct is dry and make sure to seal all joints with approved tape.

Now there are spray on duct sealers that also insulate so do your reseatch on Google to find out more info.

If the exposed duct that is sweating is supplying conditioned air to the warehouse, and is not internally lined with insulation, then a 2"-3/4# FSK fiberglass duct wrap will work just fine, as hvac1000 suggested. If it has internal liner, then the temperature differential between the warehouse space air temperature and the duct supplied air temperature is too great and adding external insulation may or may not help. It may take adding insulation to the building in order to keep heat from building up, or increasing the size of the conditioning unit if it is undersized (hvac1000 can verify this, I only know insulation).