I was assuming OP wasn't that clueless - but even if they are (and I know there are people like that, and I get the frustration), snapping at the junior person directly is really counterproductive. Especially in the context of the rest of OP's situation, it's clear that they're not getting any structured instruction, and if you throw a lot of stuff at someone in a haphazard way they're not going to retain it. My current job had a really disorganized onboarding process, and 18 months later I do occasionally still have to ask for reminders about basic Jira processes or test/deploy setups that I don't use every day.
My response would be to answer the question when they ask it, then wait for a calmer time and ask the process questions if you need to (or better yet, ask the junior employee's manager first):
* "Hey, it feels like we've been through X a few times now. I'd rather you ask if it's not clear, but is there something that isn't clicking for you in my explanation?"
* "I was a little surprised when you asked me about X, because that's something that we usually cover in first-week or first-month onboarding. Was it not covered then? Is there something unclear in the documentation from then?"