My son was driving home and he smelled a sweet smell. At home, coolant is dripping from under the truck. We popped the hood and coolant had sprayed all over the engine compartment. With the truck off we saw no active leak, with the truck on we saw no active leak. Refilled coolant and let truck sit. Now the resivoir is empty with a puddle on the driveway. Visually and manually inspected both radiator hoses but didn't see any leaks. Where else can we check or do we need to pressurise the system and check?

Yes, pressurize the system and check. The source of the problem should then be apparent.