This rod still has some life so any tips to fill in this missing chunk of cork?

You can use golden oak wood filler in layers. Option two and arguably better, cut out the damaged ring at the seam, (you can see it if you look closely), drill a new ring to diameter of the blank, split the ring, epoxy in place using zip tie to clamp, file, sand to final shape. 

I once read an article in an old fly fishing book. Sometimes flies (and lures) get yanked out of a cork handle leaving a hole. It said to take some cork from a blank or old handle, Grind it into powder with 80 grit sand paper and mix with just a drop of wood glue. Make it the consistancy of bread dough or such, then mold it into the hole and sand smooth with very fine paper. You might have to wrap blue tape around it to hold the paste but I think it could be done.

I’ve used sawdust and glue but not for a place that bad.  Go with DVT.  His recommendation is good.

1 hour ago, N.Y. Yankee said:

I once read an article in an old fly fishing book. Sometimes flies (and lures) get yanked out of a cork handle leaving a hole. It said to take some cork from a blank or old handle, Grind it into powder with 80 grit sand paper and mix with just a drop of wood glue. Make it the consistancy of bread dough or such, then mold it into the hole and sand smooth with very fine paper. You might have to wrap blue tape around it to hold the paste but I think it could be done.

This works but wood filler is the same idea just less work

23 hours ago, Delaware Valley Tackle said:

This works but wood filler is the same idea just less work

Probably what I read was written before they had good commercially available wood fillers.