I work as a junior backend developer at a company. It's been two months now. Ever since I joined, they wanted me to pair program with another senior developer. However, since the deadlines were near, this Mr. Senior decided to delay explaining the codebase until after the release. Fair enough. (I've tried to read as much of it as I can but there's too many moving parts and it's hard to understand what goes where.)
So now that all has been done and dusted, he's still reluctant to explain what the code does. (It's a lot and it's spaghetti). I tried being upfront and telling him that I'd require him to explain to me what his code does because Mr. Manager expects me to make changes to it. Mr. Senior came up with the most bizarre excuses and declined.
He wants me to just stay away from his codebase.
Do I escalate this to Mr. Manager? (and potentially make enemies with other devs) or what'd be the right way to deal with this?