In my sink pop-up stopper, the tip of the pivot rod is broken, how do I fix it?
If you have actually snapped the rod but have enough length to spare you should be able to move it forwards, however are you sure this has happened?

The reason I ask is that I had similar symptoms, but all that had happened is that the rod had slipped back through the clevis strap so it no longer connected with the stopper. The clip holding it to the strap made it look like it was just broken, but I eventually figured it out.

Admittedly, on mine there is no hook holding the rod to the stopper, it simply pushes the stopper up, and gravity lets it fall again when you pull the plunger up.