well, if you apply the "common, ordinary, dictionary" definitions:
(1) an "apprentice" is someone who is still learning a certain trade – and whose work must be supervised by someone more knowledgeable ...
(2) a "journeyman" has gained enough knowledge and experience in a certain trade to be allowed to work unsupervised ...
(3) a "master" has gained enough knowledge and experience in a certain trade to be considered qualified to teach it to others ...
so ...
going further: in my personal opinion (for what it's worth) a "journeyman" should be able to satisfactorily handle an assigned project on his/her own – without constant supervision ... in simplest terms: "here, take the ball and run with it – and let me know when you're finished" ...
your original question wasn't quite clear ... did the job posting say:
(a) "journeyman level in PLCs" ... or ...
(b) "journeyman level in PLC programming" ...
based on your answer, there could be a significant difference in the specific job skills that an applicant would be required to have ...
looking at the other requirements that you posted (electrical, plumbing, carpentry) I'd be willing to bet that "PLC programming skills" are not really what this particular employer is looking for ... smart money says that the job involves something more along the lines of: "go find out why the PLC won't turn the pump on – and get it working again" ...
aside: I apologize in advance if I have offended anyone with my gender-specific terminology ... I considered substituting "journeyperson" to be politically correct – but that seemed to be a trifle "overdone" ...