3 things, some of which are probably more than one item. And with a lot of overlap between them...
1) The ability to think on your feet.
Anyone can memorize facts and numbers but they can go obsolete. A good engineer will be able to work things out. The most important parts of an engineering degree aren't the facts, it's the ways of thinking about those facts that matters.
When interviewing someone I will ask them an engineering problem that I have no expectation of them being able to answer. (I warn them that I don't expect them to know, this isn't an attempt to make them panic). I'll then slowly give them the information they need to solve the problem and see how they think their way through it.
Getting the answer isn't important, being able to come up with ideas on how to get to the answer is. It doesn't even matter if the ideas or approach they come up with would work or not in the end as long as it is practical and not obviously flawed.
2) A willingness to learn and adapt.
You'll never know everything you need to know since technology is always changing. An engineer that wants to always stay in their comfort zone using only parts and techniques they are familiar with will soon be useless. Similarly you need to avoid clinging to your own ideas or rejecting ideas due to the "not invented here" mindset, I've seen many projects ruined by that.
This has to be tempered with the ability to balance risks and benefits of different approaches. New and shiny is great but the costs and risks involved don't always justify it even if it would make the project far more fun.
3) I don't care if it's generic, you've got to be a team player.
I've seen incredibly capable engineers passed over for jobs because people didn't think they would work well with the rest of the team. Engineering is a massive collaboration, working well with and communicating clearly with others is as important if not more important than any technical skill. And not just with other engineers, you also need to be able to communicate technical things to non-technical people at times.
You've got to know your strengths and weaknesses and those of the rest of the team, don't spend hours on a problem that someone could tell you the answer to simply because you don't want to look stupid. No one expects a fresh graduate to know much beyond the basics, there is a big difference between theory and practice, knowing when to ask questions is important.
Argue your side in strategy/design meetings but once a decision is made stick to it, don't complain or try to work around it. And try not to say I told you so too often if it turns out your were right and the decision was wrong ;-)