How can I tell when the wax has been removed from citrus fruit?
The best way to remove wax from citrus is simply to wash it with dish soap under warm, running water. Don't obsess about how long you should wash the fruit; usually the wax application is very thin and quickly removed.

There is no easy way to tell whether you have removed the wax, so if you return citrus to fridge after removing the wax, you might want to add a sticker to the fruit, or somehow indicate in another way that it has been washed, so that you know to use that piece of fruit promptly.

The true indicator that you have removed the wax is that the citrus will spoil more rapidly :(