I assume you're wondering what you need to know in order to be able to communicate with and judge the skill level of hackers. The former isn't too hard. Most hackers are happy to start by explaining the basics if you have no clue what they're talking about. Exactly what details you need to understand depends on what you're working on. You should understand the overall concepts behind the design of your product.

For a non-hacker to judge the skill of a hacker is nearly impossible - it's hard enough for hackers to do it. PG discusses it at length: http://paulgraham.com/gh.html