You are very close.
In your first line of code,
you are finding the value , but not the index , of the maximum. If you call max() with two output arguments, then you will also get the index.
>> [max_num,max_idx] = max(K(:));
In your second line of code,
>> [X Y]=ind2sub(size(K),max_num);
you are using a function that converts a linear index to (x,y) coordinates. But you have not put the index into that function; you have put the value into that function.
I think that should get you there.