There are 12 inches in a foot and 2.54 cm in an inch so 16 feet is
16 12 2.54 = 487.68 cm
Thus you can fit 243 sugar cubes along the length of the truck. Similarly you can fit 121 sugar cubes across the width of the truck. For the height 4 12 2.54 = 121.92 cm but a dump truck is open on the top so I think you can stack 62 sugar cubes. Thus a block of sugar cubes 243 by 121 by 62 will fit on the truck, that's
243 121 62 = 1,822,986 sugar cubes.
By the way, if you are just going to dump the sugar cubes on the truck then some will break and they won't fit nicely together so I don't think you will get 1,822,986 on the truck. I hope you have a lot of help to neatly and carefully arrange the sugar cubes on the trucks.
By your email address I expect you are in the USA so a trillion to you is 1,000,000,000,000. ( a trillion doesn't mean the same thing everywhere. Go to the first page of Math Central and search in the Quandaries and Queries section for the word trillion and look at Billions and more!)
To find the number of trucks needed divide a trillion by 1,822,986.