This might be an unpopular opinion, but I would expect that each newly hired developer (be it junior, mid-level, senior) can and will take time to do train and improve him/herself. I don't mind this being on job time, as long it is not all day. Most times this is even required when doing a task, because no one knows everything, even with X+ years of experience. If this mindset is not there and a newly hired developer…
Having talked to others, though, I find that a lot of folks don't necessarily realize that this is acceptable/encouraged. As I moved into senior roles, I tried to do a better job of conveying this. And overall, employers and managers need to do a better job communicating that doing this is expected/reasonable behavior.