Most smaller private jets can be flown single pilot, as long they are not flown under commercial ops at least under US regs. Larger jets with two required crew members will always have a fully qualified co-pilot capable of flying and landing the plane.

Jets are complex however, and are very picky on airspeeds and flap/slat configurations on landing. Even a pilot, not rated for the jet in question will have a tough time pulling off a landing without bending some metal. The chances of a non pilot pulling off a survivable landing are fairly slim, without some serious side by side coaching.