Measuring voltage on an analog pin - What do I need to know about amperage? I'd like to measure the voltage at a test point on a stepper motor driver chip with an arduino. The voltage at this point controls the amperages to the phase coils and is adjusted to trim the driver.

I have a common ground with the driver already, I'd like to wire the drivers v-ref point to an analog input to drive an LCD showing the output amp number so I can adjust the driver.

The issue I am worried about is that with the hardware I have to test with a properly trimmed driver is pushing 0.84A.

Is this safe to do without killing the arduino board?
Yes. The only thing you need to be concerned about is the voltage. It needs to be less than the Arduino Vcc.

The voltage sense circuit (analog inputs) typically have a high impedance and should draw a negligible current from the circuit being sensed. I didn't have much luck finding the actual spec for any of the AVR chips, but I did find this answer to the question on Electronics.StackExchange – where they say "hard to tell, the specs are incomplete, but 10 KΩ seems like a reasonable guesstimate/assumption" (I paraphrase). The reasoning is interesting and worth a read.