Need to help understand Call job instruction

It is not F0, the Argument or parameter reads ARGF, then the value follows. In the called job you should see GETARG instruction which will assign that to a local variable in order to do something with it.

Like this: GETARG LR000 IARG#(1)

If you see in your job, (JC_AGCCK.jbl), there are GETARG instruction, when the job start for work and receive to this instruction, it will give value defined for ARGF0 tag and save in one of variables same as example that Lemster68 say in up.

for more info about Yaskawa instruction, read Inform manual.