Which espruino hardware to read rs232 NMEA data from external GPS (Novatel Flexpack6)

'but I can't find any pin labelled /marked as UART/USART marker.'

the schematic might provide some assistance:

found below the tutorial image icons beneath heading Information
https://www.espruino.com/Pixl.js#informa­tion

https://github.com/espruino/EspruinoBoar­d/blob/master/Pixl.js/pdf/pixljs_sch.pdf­

You actually mentioned the Tx/Rx reference D0 and D1 in post #4

'Ok, so I checked Pixl.js documentation. I didn't get anything'

I'll agree that the docs (diagrams for hardware SPI/I2C/USART) are more suited for the STM family, the earlier Espruinos, when the Nordic nRF micros came about, it did take me some time to grasp software SPI/I2C/USART as it can be used on any pin. I'd re-read over the USART link in post #2 and just stick with it. There are plenty of examples and tutorials.

Remember: should you use the hardware USART the Pixl will have to give up B.T. comm which shares that Serial port