Are there any traces that can be turned on to see what XCALL sql is actually doing?

Oddly enough, no. I guess the theory was that you could use the database trace options implemented by the database itself for that purpose.

For ODBC, you can activate tracing via the SQL_SET_CONNATR opcode, using the SQL_ATTR_TRACE and SQL_ATTR_TRACEFILE options.

For MySQL, I believe you need to activate it via options in the configuration file. The default configuration file is my.cnf, but you can change it with SQL_SET_CONNATR using OPT_MY_READ_DFT_FILE.

I must admit that I've never actually experimented with either of those, so I'm not quite sure how useful the tracing is or how you adjust the level of detail.