This is a variable you get to use when you have a column changing event.
It will be what the column is changed to, in your case, the JobNum.
Honestly, I wouldn’t hook into the column changing event.
I would make a new event with a trigger of DataTable > Column Changed* > ReqDetail > JobNum and then use your original syntax for the BAQ of ReqDetail_JobNum = '{ReqDetail.JobNum}'
It sounds like an event timing issue. Using the changed event will allow the view change to actually happen and then you can access the view field.