I don't entirely understand your second question - surely the second question is how you'd access this with SKILL? If you do that, and then do:
plot(value(getData(“/AVDD33” ?result “tran”) “Cload” 2e-12))
you'll get what you want? For the first, I did this:
drGetWaveformYVec(value(getData("/out" ?result "tran") "CAP" 1.5p))->expression
and it outputs:
value(getData("/out" ?resultsDir "/export/home/andrewb/demos/OCEAN/simulation/ampTest/spectre/schematic" ?result "tran") "CAP" 1.5e-12)
(my expression was similar, but not identical to yours).