This is a short list, off the top of my head, and I'm sure others will add, or comment, but... Remember, assuming Junior, and that others are willing and able to work with the 'Junior' person to mentor them, that this list means to 'at a minimum, understand basics of'.
Personally, I'd expect them to understand concepts and things like :
-Privacy and regulatory laws
-Knowledge / acceptance / admission of what they do and don't know (in the event they're working in a team atmosphere)
They should, at a minimum, understand fundamentals (even if not knowing exactly 'how-to') of:
-What a buffer-overflow is and how the stack works
-What privilege escalation is
-The OSI layer (at least a good overview, at a minimum)
-How network protocols work
-IP addressing fundamentals
-Types of web-based attacks (even if not knowing HOW TO, such as SQL injection, authentication bypass, CGI / PERL exploitation, etc.)
-Understand what types of encryption / obfuscation exist, and their uses (even if not completely understanding their inner workings.)
-Minimum basic understanding of routing and switching
IMHO, they should also be at least somewhat comfortable with some sort of scripting language (whether dos batch scripting, Windows PowerShell, *nix BASH, etc) and not be 'afraid' of a command-line.
Those are starter items, and by all means, not all-inclusive. I'm sure, as I sit and think, others will come to mind, but since this is a forum, I'm sure other folks will chime in, too.