You should check the return values from your calls to nrf_drv_twi_* functions. I would also recommend you to check the return values using APP_ERROR_CHECK(), and follow this debugging method to see if any errors are reported. Have you tried setting a breakpoint in the event handler, to see if it is called at all? Are you using softdevice in your application, and have initialized this before calling sd_app_evt_wait()? In your call to nrf_drv_twi_tx() you have set the no_stop parameter to false, but the datasheet seems to not expect a stop condition between tx and rx in a read operation. Have you tried setting this to true?
