What is the best thing for me to do right now ?
(Dripping him vitamins every 5 hours or so)
How long ago did he hatch?
Best thing to do is leave him be. The cord will come detached once the duckling starts moving around more and will break it off himself. No need to drip vitamins yet, ducklings have enough nutrition to keep them going for a couple days after hatching. It's best not to give them food or water until they are on their feet and moving around on their own (24 hours old or so).