Which altcoin would be the easiest to fork a cryptocurrency from for educational purposes? Which codebase would you recommend for a novice who wants to create and run an altcoin in order to understand the technology - like a student compiling their own version of MINIX in order to understand operating systems? 

If you want an objective criterion for difficulty, that would be how many lines of code are in the repository, not counting common libraries. Personally, I'm not interested in implementations in languages like Python that are considered easy to learn.


Litecoin is a popular choice, but SegWit won't make it easier.
I know Cryptonote is a more complicated protocol than Bitcoin. But what about Nxt, or other cryptocurrencies developed from scratch rather than copying Bitcoin?
Would Ethereum be relatively comprehensible if you removed the smart contract/EVM code?
I know there are tools to generate your own altcoin, but that would defeat the educational purpose, wouldn't it?
You could take a look at Jeremy Rubin's TinyCoin:
https://github.com/JeremyRubin/tinycoin

It is, exactly as the name suggests, a very small cryptocurrency written in python which is designed purely for learning purposes. Might be what you're after :)