By sharpen you mean to take a relatively flat image and to boost contrast?
If so, using the color boards with scopes that ship with FCP can probably accomplish what you're looking for. (Often times simply working in the exposure tab with wave forms set to luma is sufficient.)
Here's some more info.
Michigan One Fly wrote:
… but how do I sharpen it in FCP X ?…
effects/blurr lists a basic sharpen filter
for a much more elaborated control (luma sharpen, sharpen edges etc), FXFactory Pro lists some 'sharpeners' - 399$
plug-in master creator Alex lists a free unsharp mask (=this does NOT mean 'blur'!) tool, like in Photoshop, here
I may profit recommending fxFactory