Thermoelectric Cooler sensor
If you want to measure the power to only the peltier, do one of these things:


Put the fan on a seperate supply
Get 2 mulitmeters (one for voltage and one for current) and connect them to the peltier (current in series and the voltage across the peltier)
If your fixing the voltage to the fan and peltier the fan will be a fixed load and will not vary, if you can measure the current to only the fan, it can be subtracted from the value on the power supply to find the peltier current (assuming that the fan and peltier are in parallel with the supply, don't run them in series).