Put a drop into the 'seam' between the blade tang and the forward end of the lockbar, where the two come together with the blade open and locked. If you want to, you could also put a drop at the lockbar's pivot pin, at/near the center of the back of the handle. And the blade pivot itself can be lubed with a drop onto the rounded end of the tang, with the blade closed.
With any lube, keep it very, very light. Using too much will just attract more dirt, and gum up the joints.