BQ40Z50: What should I do to make this fuel gauge circuit work?

You need to first calibrate the evm, following that you need to perform a chem ID selection following the instructions on the GPCCHEM page. Then you need to configure the gauge per your application settings and then perform a learning cycle. The instructions for the bq40z50 are similar to this pdf, www.ti.com/.../slua777.pdf.

schematic looks OK to me. You can't use a 12V for a 2s pack. Open up bqstudio, select gauge, select bq40z50-R2 and open the advanced comm tab in the bqstudio program. In it read word 0x0D. If it returns 0x9000 or something and doesn't nack it, then you need to program fw. Else your IC may be dead.

Depends on your max cell voltage. If your cells are 4.2V Vmax, you need 8.4V, if they are 4.3 or higher, multiply that by 2 and use that voltage.