In Black Ops 3 script debug information are located inside their built FastFile**.
All you have to do in order to print any S.R.E. (script runtime error) is to set either dvar:
- developer 1 / 2 – Enable developer systems for Mod Tools.
- logfile – writes all console log information to current fs_game location (i.e. mods/modname/console_mp.log).
** NOTE: The base game doesn't have any script debug information, if you're getting a SRE from another script that's not built into any FastFile from your mod tools you will need to include those scripts into your zone file as well.