I don't think you would be able to do that through JTAG. If the UART pins are used why are you not using I2C or SPI to send these debug messages.
I should have stated it more correclty. I was using UART to get debug messages and had to give up it also along with SPI.
BTW how to interpret the debug messages on the I2C? Can you please recommend any product/tool for this? I searched and found some but do not know which one will be suitable for this.
Any I2C bus monitor should work but you'll have to decode the hex and see what is being sent (That is the main advantage that UART has, you've utilities do the decoding for you)