OK, I'm awake now and ready to go. Hi, Eddie. You really don't have to go to too much trouble to find out what is on your teak. It is probably some kind of oil but teak is so naturally oily that even if it isn't, the surface will have an oily feel unless it has received some kind of film finish. So the only question in this test is if there is oil or wax on the surface. Naptha will remove the oil or wax. Wipe the naptha on with a rag and see if it washes off the finish. Be sure to do this outside and out of direct sun. Also, be sure to stay away from sources of ignition since naptha is extremely flammable. The rag will absorb the oil or wax if they are present so change the rag you are using often. When you are through, be sure to leave the rags outside and loose--not folded or wadded up--until they are completely dry.
If it is obvious that the finish is not coming off with the naptha, then it is a film finish and you will have to strip. Choose a relatively safe stripper and read and follow the label directions. As you may have guessed, I think that Citristrip is a pretty good and safe product. Personally, I will not use methyl chloride based strippers. They work well but I am concerned about the health effects. Whatever product you choose, be sure to wear rubber gloves and eye protection. And read and follow the label directions on any of the chemical products.