Using internal ngspice:
Add a .control section to your eeschema diagram as a text file. It may look like this:
.control
* wait with the following commands until simulation has finished
set controlswait
* save the name of the current plot into a variable
set prevplot = $curplot
* do an operating point evaluation
op
* print the data
echo Data from $curplot
print all
* go back to the previous plot
setplot $prevplot
.endc
For the notion of ‘plot’, please have a look at the ngspice maual, chapt. 17.3.
External ngspice (if you are with KiCad 5.1.5):
Eeschema->Tools->Gernerate Netlist File->Spice
Enter path and name of ngspice simulator
Run Simulation
ngspice window opens up
Run
Evaluate the data
You need the allowance to write to the directory where the project is located. I have tested this with MS Windows.