Can I laminate on top of an existing laminated countertop, assuming the old surface is secure and sound? Is there any special prep work need to the old laminate? Is there any special contact cement required for this application?

Yes,you can apply new laminate to existing surfaces.

Sanding the old surface is recommended,then applying rubber cement(contact cement) to the cleaned surface and by putting it on the new laminate as well,be careful, using round rods to keep the 2 surfaces separated,align the new over the old,with overlap all around outer faces(to be trimmed later for a snug fit)

Then, by removing one rod at a time, slowly drop the new surface to the old(you must allow the cement to partially cure for a permanent bond)

Trim the overlap edge with a router or block plane with slow strokes as not to chip or break the laminate.

Hope this is helpful,

KBC