ADC on PIC32MX575F512H
The circuit you're trying to adapt is for measuring the power rail voltage. The circuit you've drawn is pointless because you're measuring the current through that voltage divider, which will never change. \$R_{sense}\$ needs to be right after the 12V regulator, and be sufficiently small to not dissipate a bunch of power or drop a bunch of voltage. You need to make that call based on your expected current draw. Generally you'll want it to be small, probably less than \$1\Omega\$, and put it into a current sense amplifier, like a MAX4732. The output of that amplifier can go into your ADC.