Destroy cargo in Port was a mission in Jak II. After catching the scouts in Haven Forest Jak received a call from Krew, who heard from his racing client that Jak was pretty good with that JET-Board of hers. A shipment of Krimzon Guard listening equipment had arrived in the Port and he needed Jak to get rid of it (both for him as well as the Underground).
Once you arrive at the port you'll see a large number of green blips; signifying the cargo that needs to be destroyed. Each cargo is surrounded by mines that explode shortly after being touched or when something gets too close. There is a timer of 2:15 minutes, which starts as soon as you hit one of the cargo (there's 16 total).
The image here can be used as one possible guide on which course to take to destroy all the cargo, although a quick survey with a zoomer can make it easy to see the layout yourself. You'll need to use the jet board to move around and hit the cargo while avoiding the mine, making it more centered on precision control. You can use tricks or jumps to go faster or avoid mines as well.