Nobody can deny Jenkins' obvious qualities. He's the kind of guy you expect to see on the Baltimore Ravens roster - full of passion on the sidelines and on the field, he's a true leader. Not happy playing a bit part in the backfield, he'll push up to the line of scrimmage and take on a running back in run defense. Great vision, he reads the quarter back like a dream and has that ability to turn an interception into six points. Not always the greatest wrap up tackler, but he certainly puts in maximum effort to get to the ball carrier.
But these qualities sound more like you're describing a talented safety, not necessarily a lockdown corner. Critics have questioned Jenkins' recovery speed and his ability to stay with speed receivers. It doesn't take much research to find evidence of this, watch a few Buckeye games and the one noticeable criticism of Jenkins is how often he's struggling to stay with a wide out on a deep route. In the college game he often got away with it due to an under thrown ball, he won't have that luxury in the NFL.
So he'll take to the field in Indianapolis hoping to prove to scouts he's got the speed to warrant consideration not only as a corner back, but also a top 10 pick. A team will be reluctant to take Jenkins as a project safety and he'd need to add bulk to make a smooth transition to that position (despite having height - 6'1" - he isn't the biggest, and lacks that sledgehammer hit you see so often from pro safety's). If he runs well in the 40 yard dash he'll justify a high pick as a potentially elite corner and may even warrant consideration by the Seattle Seahawks with the fourth overall pick.
The Seahawks have invested picks and money into drafting Kelly Jennings and Josh Wilson, whilst also re-signing Marcus Trufant. Another big investment could make the position a little top heavy, but GM Tim Ruskell has spoken of finding an 'impact' player. Jenkins has no obvious character flaws and stayed at Ohio State for his senior year - he's the prototypical 'Ruskell guy'.
But he has to run well today, I don't think we'll see a more crucial 40 yard dash this year.