If you want to do things like that you run it in command line mode (by running tgdcli.exe instead of the normal tgd.exe)
This will spit out basically everything terragen does as it does it. From preview render workings, to objects being populated, number, shaders added, everything. If anything it might be nice to turn off preview rendering pass information (as it spams you starting pass 1, 2, a TON lol)
Also, if you want to be able to copy/paste those logs onto the forums, you could run from command line
(path to terragen)/tgdcli.exe >> mylog.txt
It will print everything into the file instead of to the console, which will allow you to upload it here nice and easy. Might be useful to catch where something might cause a crash.