A 1RM test is simply is simply a way of estimating the maximum weight you could lift for an exercise one time by using a calculator. For the test to be accurate you need to select a weight for an exercise that you can only do about 10 times. A weighted vest is usually too light to cause failure for an exercise within in 10 reps. Also, most vest are not adjustable in weight, so taking a 1RM test with a weighted vest in most cases would not work.
Wrist exercises are normally done for many reps and a 1RM test would not make a lot of sense. A 1RM test can be used for a lower body exercise like a barbell squat, but I would not suggest doing a 1RM test for lower body exercises where the main weight load is your body weight or where balance and form are difficult.