You need to take a Nautical Institute approved basic DP operator course and obtain 30 sea days of DP watching standing aboard a DP Class II or III vessel.
As a midshipman you'd best be served taking DP basic either during your summer or after one of your sea years, preferably after the first sea year. I would then suggest during your second sea year argue like the devil with shipboard training to do 30 days on a Class III DP Ship (6th generation drillship preferably).
Also it's not a must for hire but it helps to take HUET Training.
The more training or sea time you have towards a DP Basic Certification helps obtain a great paying job.