The lenses have tabs. You have to look very closely for them, then squeeze the lens out of the holes.

What usually happens is a bulb gets way to hot and melts plastic parts.

 

Actually, that rear cargo lens needs a flat screwdriver to open it. Insert the screwdriver in the slot(red arrow) and pop the lens loose.
It's a little tricky to put back in place and easier if you use the screwdriver again to close it.

 

FMG to the rescue!! that's what we needed to address this bulb access issue, thanks for the pictures, was this your SS in the pictures

 

Yes Oldblue.
Since the OP has a 2010 model, I figured mine would be the same.

 

FMG, that's just what I hoped to learn, thanks! This will be my Saturday morning project; I'll report back as soon as I'm done. (I'm in Southern California, and it's projected to be in the low 70s, and sunny - perfect to work outside.

Whoo hoo!

 

Well, I think I've found the problem. Not only was there no bulb/lamp at all, I'm not sure the wiring's there. I wonder if because it was built as a fleet/rental car, the cargo light just wasn't connected?

Here's what my cargo light looks like, opened:



The casing/lens unit removes VERY easily (slide one end out, then the other).
There is a plug, but it doesn't look compatible to the correct lamp. It has three tiny holes for connections. When I do that, here's what I see:

 

Yup, there's a few pieces missing! Can you use a test light to see if there is current from the red to the black wires in the connector?
Is it door switched? Or hatch switched?
Please remember to have a lovely assistant be there to open the hatch for you, there's no inside handle!

 

Yes, there's power to the connector, and it's door-triggered, not hatch-triggered. Power dropped to zero as the front dome light dimmed to off, after the door was closed. (And thanks for the tip about the lovely assistant - I just dropped one of the rear seats, and used the regular doors...)

 

So then maybe you could wire in an LED like this adhered with double sided tape

2X 12V Car 48 SMD White LED Light Panel T10 Festoon BA9S Dome Map Interior Bulbs | eBay

I had one of these in the back of my old pick'em up for light at night in the bed, I taped it to the underside of the fibreglass tonneau cover, it was very bright! The light not necessarily my idea!

 

Interesting idea about those LEDs!

Or could I pick up a replacement cargo light (with wiring) at the local junkyard or on EBay?