The port at both sides of the connection must be at the same setting…unfortunately tools to query a port’s setting only tell you what the driver is set to, and the hardware itself is not able to verify it is in that mode (or if it is capable of that mode).
On your host side, if you were to tie the RX and TX wires together you would have a local loopback. Your serial console application, if working correctly and at the settings of the port, would echo anything you type back to you. I suggest verifying this way on your host side if you use an actual RS232 port (or perhaps even at the end of the USB cable). You can’t do this at the Jetson side since it has serial console both sending and receiving…but J17 ("/dev/ttyTHS2") would be a good sample because this has mostly the same characteristics of ttyS0 (try ttyTHS2 at 115200 8N1 in loopback by tying RX and TX together, then a serial console program to see output echoed from input).
One thing to know is that the ports are 3.3V TTL levels. Not all serial UARTs are at this level, e.g., some are 1.8V, and ordinary 9-pin D-sub connectors are far different (and in fact would damage 3.3V UARTs). If you were to use the wrong serial UART there is a good chance of seeing garbage output.