Yes and no. Anyone who is working with CNC machines professionally needs a good functional understanding of G code, even if you are rarely writing it directly. You should absolutely be able to knock out simple programs by hand, even if you need to sit there with graph paper and work it out slowly. This is more so you can look at CAM produced code and have a clue as to what is going on.
What is probably not a very high ROI skill is the ability to stand at a control and bang out anything of any complexity by hand. Even on-control programming schemes (Manual iGuide in Fanuc, Haas VPP, everything Hurco) are getting less and less relevant as CAD/CAM skills go up and costs go down. I’m not saying Finger CAM has no use or is outdated, just the number of environments where that skill is put to regular use (outside of basic turned parts) is small and diminishing. So in the end? Definitely take this opportunity to learn G coding by hand, but don’t think that if you become the hot shit Top Gun Finger CAM master of your class that this skill will mean much in the real world.
Absolutely focus on CAD/CAM skills. Those investments in your time will have a massive payoff.
For controls? The question is defined by the market you want to work in. Haas is the largest volume seller of machine tools in the US, being fluent in older and next gen controls is a base level skill. Fanuc runs a somewhat distant, but very clear, second. I wouldn’t bother with Heidenhain; by the time you have enough industry experience under your belt that someone would loose you on any machine with a Heidenhain controller? You will have forgotten everything you learned about it years ago in tech school. Same with Siemens. I would take the opportunity to work on these controls for a little bit so you can understand the broad differences and retain enough to not be totally lost when you are standing in front of one 5 years from now, but mastering them will take away from higher ROI skills you should be learning ASAP.
Focus your school time with on-machine skills that you can’t learn off of YouTube. Anyone with a little gumption can learn any CAD system, and most of the CAM systems, off of YouTube (I did). What is much harder to get is access to big capital assets that folks will let you use. Your money in school is absolutely best invested in hands-on skills. It is absolutely wasted on CAD/CAM classroom time (beyond whatever their base level requirements are). You can download educational versions of all that software and learn it at home for free.
Learn how to use a grinder properly. Learn basic TIG welding if you get the chance. Take literally every opportunity to tram in a vise and fully line in a 4th axis with a dial test indicator – those are under-appreciated, basic, critical skills that fucking save the day in actual machine shops, and lots of folks suck at it.
Also, when you are done with the trade school? Take some god damn accounting classes ASAP if you want to run your own business.