These are the sources I used:
Hope these help!
Yeah, this answer has definitely changed in the past year and a half. I know that they "archived" their user training from Atlassian University in a YouTube playlist - here's the link for that.
As for the administrator training, I haven't been able to find that anywhere.
I think that you should start with Atlassian University.
Moreover, I would follow the questions being raised here in Atlassian Answers (you can watch tags like jira-administration, for example). So each new question that has this tag will send you an email. You can of course go over older questions too. Most of the day-2-day questions were already asked in the past, so you should find what you are looking for.
And of course, Atlassian has a good knowledge base - look at the middle column titled Administer JIRA.
Most of the information is easily available on the internet and on Atlassian official website but if you are looking for a single guide then books by experts can really be helpful and you would find everything in one place. It is difficult to find one book that suffice all your needs. The books referred above are by experts and I also recommend them.
I would like to mention that I wrote Mastering JIRA last year and it has information about customizing and administring JIRA.
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