"debug" may be the wrong term, but 'diagnose' might be a more necessary skill.
a colleague described a recent scenario. they've got a college kid (... 1st year? 2nd year?) doing programming work, and basically dissing on all tech stuff that he isn't intimately familiar with (which... means a lot of stuff). he managed to get some stuff working on google app engine, but some of the stuff doesn't work. The kotlin stuff has a warm up time ("that's normal"), but some PHP stuff takes 8-10 seconds all the time for on every request. "PHP sucks, it's shitty, everyone's leaving it, kotlin rules", etc.
No one else is seeing that same performance. Most other people hit the PHP instance and get 100ms response times with moderate payloads. He keeps insisting that it's PHP that's horrible, and what he's seeing is evidence that not even google engineers can make it work because it's so bad.
My colleague and a couple others have said to him "you have a network problem - some route to that app engine isn't working right for you for some reason".
"oh no, it's not that. PHP is crappy".
So... over the holidays, he goes home to parent's house. Has a week of doing some work, never once mention of PHP being slow. IIRC, he seemed to think google got stuff working (despite PHP being crappy). Then he's back at his regular place, and suddenly it's all slow/bad again.
Hrm... if you're the only person on a distributed team having extremely slow network issues to one server, then that problem goes away when you access it from a different network, then you have the same problem when you go back to the first network... it's not the remote technology. Or... at least not the tech you think it is.
I'm not saying he can actually debug or affect an actual fix, but diagnosing/recognizing the signs of network problems as actual network problems should be a requisite. If 8 people hit a server and get 100ms or less response times, and your requests take 8 seconds from your house, but 100ms from your parents' house... this is a network problem on someone's end. It's not a PHP (or kotlin, or ruby, or whatever) issue.