I don't think you can get absolute assurance. Assuming you are querying about legal arrangements, here are a couple of situations which come to mind: in Japanese habachi restaurants (Benihana, etc.), the tip is normally split between the table cook and the server; where the cook has been very good and the server lousy, I have seen others (and done it myself) give the cook some cash at the table.

Also, where a team is serving you (a primary server, a waterboy, busser, etc.), the tip may be split; I seem to remember specifically being told about such an arrangement at one of the National Park restaurants. I had asked because the waterboy (or girl) had done an excellent job of keeping drinks refilled and I wanted to make sure he or she received a portion of the tip.