回答“Broke off tip of knife”No - there isn't any way to re-bond the ceramic material, especially in the tiny surface area of the fracture. Continue to use if you can or -sadly- discard and replace it.
回答“Looking to fix a hole in Patagonia Black hole duffel”If anyone lives near the water, check if there is a sail maker nearby. They all stock these terrific repair tapes; light nylon ripstop in multiple colors, and heavier woven fabrics in white, tan, black, etc. All have one-time adhesive already on the back. Most places would just give you a small piece to repair gear - maybe a 6pack or a box of donuts will seal the deal for sure.