read negative voltage with mcp3008
It cannot.
However, you can make a voltage divider that will make it into a positive voltage, by using a positive voltage as one side of your divider.
You say the voltage you want to measure is -12V to -9V. If you have +3.3V available, you could use a voltage divider with about a 4:1 ratio, like so (4.7:1 in this case):



simulate this circuit &ndash; Schematic created using CircuitLab
Your output voltage will be $$V_{out} = 3.3 + \frac{10}{57}V_{in}$$
So when the input is -12V, the output will be 1.195V. When the input is -9V, the output will be 1.721V.
If you have a different voltage than +3.3V or your ADC can only measure up to 1V or something, you'll need different resistor values, but this is the general idea.