Wow, that's a good one. I believe GJC is George J. Carrette (?) who worked on Macsyma (the precursor to Maxima) about 40 years ago. MACDOC;TRDEBUG USAGE
is a reference to a file on an ancient filesystem. There may be a file named trdebug.usg
or something like that floating around; I haven't looked.
I think you will find most or all of the existing documentation for debugging in the section titled "Debugging" in the reference manual. Here it is online: http://maxima.sourceforge.net/docs/manual/maxima_38.html I think that the same documentation is also included in wxMaxima.
By the way, where did you find the reference to MACDOC?