To extract parasitic capacitances or conductivities, you need to perform an AC analysis. Then, you can choose the parameter from the output file. For example if you want to extract gate-source capacitance as a function of gate voltage at a freq of 1 MHz:

solve init

solve vdrain=0.1

log outf=c.log

solve vgate=0 vstep=0.01 vfinal=0.5 name=gate AC freq=1e6

After plotting the output file, you can choose cgate>source for the y-axis and the gate voltage for the x-axis. You can take a look at the following paper:

https://www.sciencedirect.com/science/article/abs/pii/S0749603615002712

https://www.silvaco.com/examples/utmost4/section1/example18/index.html