Can someone suggest the best/easiest way to capture a CHDK screen on a Win 10 PC.
Best/easiest depends on your preferences, but
chdkptp can capture screenshots. You can either use the screenshot button, or the lvdumpimg command.
screenshots are in
netpbm ppm or pam format.
The GUI screenshot button is probably simpler, since it outputs PPM and applies the same aspect correction and scaling as the live view.
An alternative would be to use video out and a capture device.