How do you keep your ISPF skills updated and relevant in the mainframe industry?

For one who need a refresher I think regular use and practice of ISPF is the best way to stay familiar with the commands and features. For reference IBM's official documentations are available on ISPF.

The trick is to get the mainframe simulator on your PC. I have used Hercules and gotten it to work. HOWEVER, I took a while away from it and lost my userid/pw. I have been trying for months to contact IBM and retrieve it. It has been ungodly difficult. Once you get it working there are not that many screens to master. I would master 1,2, 3.2, 3.3, 3.4, 3.13, and 6 first. Others can be added on but I would consider those the main ones.

This is a little difficult if you are not working on a mainframe at a company. The integration of a PC/laptop and the mainframe has been different at every place I have gone to. It is absolutely essential in a work environment to know how to use your PC/laptop as something more than a dumb terminal. The most useful PC/software I have found in working is #1 Microsoft Office. Probably #2 is Notepad or Notepad++(even if it says you can compile though, you really can't use it as a compiler). Probably #3 is WinMerge(great for showing differences between current code and modified code). Probably #4 is Teams and/or conference software such as Zoom, Google Hangouts, and/or Webex. Most meetings now are done via one of these 4 platforms.

This one I would consider VERY difficult if your job does not use a mainframe. Hercules and similar software give you an idea of working the mainframe, but a modern mainframe has a lot of other options/features that are just not available any other place.

Assuming you are on a mainframe, yes there is a lot to play around with and learn. My suggestions as learning options would be CICS, IMS, Rexxx, CLists, and Xpediter or however the company you work for debugs programs online.

I contracted for a long time. My first permanent job was at a company that was replacing their mainframe billing system with server based, packaged software. The two servers became four, and then six, and two years into the project they scrapped the entire project as unworkable at a cost of around 75 million. That was 2000. They were still using the mainframe in 2017. Estimates at GM were that around 33% of income goes through the mainframe. To rewrite/replace a mainframe system is VERY expensive. Few colleges teach mainframe. Most of the mainframers or older and retiring soon. Even though it is somewhat difficult to learn mainframe if your current job does not use a mainframe, I believe it would be a worthwhile investment.