I copied/simplified the JCL statements from an example included in the TK4 installation (SYS2.JCLLIB(PRIMCOB1), if it matters). Somewhere in the log it says that program IKFCBL00 gives the Return Code 12. Other than that, I don't know what other information I need to provide.
The message IEF142I is produced after the step COB of your JCL procedure named COBUCG. This step is running the IBM COBOL compiler module, which has ended with RC=12. This code typically means that COBOL compiler did not finish successfully, due to one or more of thousands of possible reasons.
The detailed report (listing) on compilation issues is placed to the output location defined via //SYSPRINT DD statement of //COB EXEC step.
You need to find this compiler output, investigate it carefully, detect and understand all those specific error messages causing the COBOL compiler to stop with RC=12.
right after line (or card) 11 made no difference in the output. In other words, it is not generating any additional output that points to the reason(s) for failure.
It is not possible. COBOL compiler always produces the full compilation listing, in case it's SYSPRINT is defined correctly. At least it does so since the beginning of 1960s, with no gaps in time.
Either you must investigate your output more carefully, or present here your full SDSF output.
There is no way of guessing.
I'm 100% sure that //SYSPRINT DD has been defined somehow within the JCL procedure COBOLCG.
You need either to verify your SDSF log in full (with the expanded procedure COBOLCG), or present this full SDSF log to the forum.