I learned everything from the ground up. Served an apprenticeship as an electrical fitter, had to go and fix machines with no drawings and half a factory of people sitting around and costing a fortune - speed was essential, built control panels, designed control systems, designed HV transformers (with a supervising transformer engineer), wound motors, went and did selected courses on temperature measurement and lots of other things. Unfortunately there are very few companies around these days that can offer this type of experience for a trade certificate - most appear to 'specialise' in selected areas and do not cover the whole.
Basically I knew a heck of a lot about control systems from my 5 year apprenticeship. Then did an electronics course - left the trade and did a business and marketing management degree and stayed in management and sales for 25 years.
Had to learn basic PLC programming as I had to sell the things - step controllers for a start.
Then took on a control system design and programming role for one of my former customers. All self taught to be honest with the assistance of a few basic PLC courses and a heavy background in fully wired control systems and service and maintenance.
I guess these days I would look for a maintenance job where PLCs are used extensively and there is an opportunity to learn from others, and courses.
One of the annoyances I have is someone who has done all the courses on programming and has no practical experience or understanding of basic control systems and programs something up with all the 'whizz bang' functions without for regard for safety and interlocking.
Another annoyance is the fact that most of the jobs advertised require the applicants to 'have a piece of paper' also without regard to the above - the piece of paper quite often is the only thing that seems to matter.
It is extraordinarily difficult to find companies that cover the 'whole' these days as most tend to 'specialise'. I know of apprentices who come out of their apprenticeship and the only thing they know is how to put up cable tray and run wires on the tray because that is all they have ever been taught. The remainder of the stuff they have learned at college is not much use to them usually as there has been no practical experience with what they have learned.