The bulbs for the front and rear trunk lights are the same, so swap them.
If you open the front trunk and the light does not come on, then leave the front trunk open. Open the rear trunk and see if the front trunk light then comes on. If the front bulb is good and the light comes on when you open the rear trunk, then it is the microwswitch for the front latch. Porsche changed the design of the microswitch in mid Feburary 2000, so if you car was built before then that is the usual suspect.
If both bulbs are good and neither light comes on when both trunks are opened, then turn on the ignition key and see if they come on. If so, then the car is still in the transit mode. If the car is in the transit mode then the interior lights also do not come on, unless you turn the ignition switch on and then open the door.