Can I crush up an iron pill and put it on my skin to see if i'd be allergic to it? I have to take OTC slow fe from cvs for anemia & I'm scared of a bad reaction.

Very unlikely. Iron is naturally found in your body in the red blood cells, so almost no one is allergic to iron. When you get a bruise, the yellowish color that appears after a few days is iron from the broken down red cells. Iron can be irritating to the stomach. It should be taken with food. People can be allergic to the dye or preservatives in the iron pill, but this is rare.
No. A skin test would not be the same as side effects from taking a pill orally, particularly a medication that can cause stomach irritation or nausea. You will have to try the medication orally and hopefully will tolerate it well. I'm certain that your doctor's recommendation that you need iron to treat anemia is important, and i recommend trying the medication.