Without getting a better idea of the nature of the questions on the test, it will be hard to answer your question. But in general, you calculate the load for each one of the two units as though it were a stand-alone single family dwelling unit. Then if they ask for the service load to the duplex as a whole, you add all the loads for both units, and apply whatever demand factors are available. For example, let's look at 220.53. If each unit has a dishwasher, a garbage disposal, and a trash compactor, then you can't take advantage of the 75% demand factor when you are calculating the unit. But when you calculate the duplex, you have a total of 6 fixed-in-place appliances, and you can apply the 75% demand factor.
That is about as far as I can go, without more information about the test question. I hope you do better on your next attempt. It took me two attempts to pass my Administrator test. But that was (gulp! ) 15 years ago. The test will have changed since then.
Welcome to the forum.
Charles E. Beck, P.E., Seattle
Comments based on 2014 NEC unless otherwise noted.