Select all of the values of k that shift f(x)=x^2 to the right when f(x)=(x-k)^2

Any value of k>0 will work.

In a horizontal shift, adding a number to x will move the graph to the left, and subtracting a number from x will move the graph to the right.  If we subtract a negative number, we are essentially adding a positive number, which moves it left.  We must subtract a positive number to move it right.