Is you Nano 8MhZ or 16Mhz ?
Attached is a working sketch for five digital pots . It doesn't use Clockdivide or setSPImMode and it uses MSBFirst so I have to ask
why Mode 2? , Why LSBFIRST ? and why Clockdiiveby 2 ?
Look at the timing diagrams on your datasheet just to confirm you have all that correct and try experimenting with different changes of the three parameters I asked about. Google to see if you can find any example code for that chip (I couldn't).