Dictionary.com defines a Nexus as:
1. a means of connection; tie; link.
2. a connected series or group.
3. the core or center, as of a matter or situation.
4. something to do with cell biology that doesn't match/isn't as applicable as the other definitions, so is being left out. Look, a monkey!
Basically, in the workplace, you don't want to know everything, you want to be the person who knows who knows everything. Other than being really hard to parse, that sentence incorporates the definitions 1-3 above by making you the center, a means of connection and part of being a connected group.
No one who is rational ever expects that you will know everything. But, for example, in interviews people will want to know what you will do when you run across something that you don't know what to do with. The proper answer is "find out what to do with that thing" and then provide examples of how you'd do that.
That seems very common sensical, but, as you know, common sense isn't (to continue with my theme of hard to parse sentences). Most employers would like a base amount of information in your brain when you start, just like your current employer wants you to know enough about your job to do it, but they also want to know that you are prepared to help yourself if you run into trouble.
What works for me, and makes me more valuable to the people that I work for, is that I retain the answer and who provided it each time I have to find an answer to a question; I keep it in email, in my brain, I make notes in my notebook...at one job, I actually kept a database of answers and who knew them. The gist is, you want to become informed beyond just being able to do your own work, but to be productive and useful to other members of your team and to be the go-to person for folks outside of your team, as well. Even if you don't know all the answers, most people don't differentiate between you being all knowing and you being the person who knows the people who know. It reflects well on you and your team, makes you a better candidate for job retention, and can be called upon for a yearly review with concrete examples to prove your value to the company.
As a manager, it makes you seem wise and mysterious. Ok, mostly just wise. Upon occasion your people will still come to you with questions where you cannot easily, on your own, go and find out the answer and those occasions can be opportunities instead of challenges, by mentoring the employee who wanted to know in the way of finding out...and then having the employee report back to you when they have the answer. You'll both be happy--he or she will have the answer they want and you'll have another fact in your arsenal for the next time someone needs to know something.