In two-dimensional even parity, how do we determine the corner parity bit? In two-dimensional even parity, how do we determine the corner parity bit? 
Here's an example:

    1  0  0  1  y

    0  1  0  0  y

    0  1  0  1  y

    0  1  0  1  y

    x  x  x  x  z


Finding the parity bits where the x's and the y's is fine, But what about the parity bit in the lower right corner (z)? Do we look at the number of 1's in the corresponding column and/or in the corresponding row?
Do we look at the number of 1's in the corresponding column and/or in the corresponding row? 


Yes; you can do it in whichever direction is most convenient; it'll be the same either way.

In either direction, the parity of $z$ will be the parity of the entire data matrix (1 if there are an odd number of 1's, 0 if there are an even number).