There are 2 recognised types of Grip in crown green bowls: Cradle Grip, and Claw Grip.
In reality, most players tend to use a Grip that lies somewhere between the two.
Which Grip you use comes down to personal preference and comfort. The most important factor is that you have full confidence that you won’t drop the Bowl or Jack during the Delivery.
To do a quick first test on your Grip, hold your Bowl in your the Claw Grip and then stretch your arm straight out to one side, with the Bowl facing up. Now turn your hand over so that the Bowl is facing down. You should be able to comfortably hold the Bowl in that position for a couple of seconds before you turn your hand facing upwards again. There should be no stress in your hand, no white knuckles, and no shaking. If there is, consider trying a smaller or lighter bowl.
Now test again by holding the bowl out behind you as though you were about to bowl it, but hold it at the top of a big backlift so your arm is almost horizontal. You should be able to hold the Bowl there for a second or two without dropping it, wobbling or twisting your wrist.