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Java, JavaScript or python would be my advice. But I've stopped coding in 10 years however I'm consulting on apps and most are using this three

Or get very basic c++ course yo understand the "object oriented programming" concepts then explore java /c# and then see if that works best for him and once he has a decent level he can move to python/Javascript which are a different type. Also learn bash for os scripting and command line processing is recommended for overall basic understanding for later

For what it's worth, my son started coding on Khan Academy for free about 6th grade. Later he took classes on Udemy and Coursera. This year (his senior year) I had him take Coursera classes on machine learning, Android App development, and he will soon be taking one on coding block chains so he can learn about some of the up-and-coming areas of coding to figure out what he wants to specialize in. Coursera classes are not for credit, but do include some certifications. Many are taught by college professors. His machine learning classes were taught by Andrew Ng of Stanford.

This would be a way to prove knowledge without the cost of college or having to waste time and money on classes about subjects that he doesn't need.

If he hasn't done any coding, starting with the free Khan Academy might be best to make sure he enjoys it before spending money. Based on my research but not experience, Coursera is well thought of by computer science companies.

Python is popular and has a lot of utility across industry. GO is another that is growing considering the mobile app industry.

Python, SQL, bash. My two sats.