You can do this by writing y{k}(end) to grab the end of the kth item. Like this:
% Make some random vectors:
y1 = [ 1 2 3];
y2 = [ 1 5 9 12];
y3 = [9 48 2 1];
% create a cell array of them:
x = {y1, y2, y3};
% grab the end of the second vector:
k = 2;
x{k}(end)