On grip shifts, the hole is on the edge of the rotating cuff with index markings on them, but often underneath a rubber shield where you can't see them. If you thought threading cable was hard through new housing, wait until you try threading the grip shift! It's not hard if you prep. I start with clean raw cut cable. I take standard solder and soldering iron and heat up and melt just a tiny bit on the tip of a clean cut cable and let soak into strands of steel. Let cool. Now this has united all the fraying strands and it becomes very easy to thread the cable through.

BTW, I thread the cable through housing with the last cap off. Push the cable out, lube with grease the portion of cable that will remain inside housing, and then slide housing up, slide the last end cap too, and then find a way to compress that cap snug onto the end of the housing, and then attach the derailleur cable to the derailleur.