Centre of K-Space
There isn't one! K-space is a 2D plot of spatial frequencies, and so there is no positional relationship between points in k-space and points on the image. Every single point in k-space contributes to the entire image. To understand this properly, take the first k-space tutorial on this site, and be more familiar with what the Fourier transform does. Briefly: the Fourier transform relates k-space to the MRI image you know (and love!).
Remember that the data in the k-space array are spatial frequencies, not intensity values with (x, y) coordinates in real space. We can plot the k-space data like we plot the array of intensity values of an MRI image, to give us something to see. But it's not an image in the usual sense.