Micro:bit acceleration

First of all, what is this measure unit?

It's in g

How can I get degrees?

I believe this should work:

var a = Microbit.accel();
print(Math.atan2(a.x, a.y)*180/Math.PI)

And....is there a way to get X, Y and Z separately?

As above you can save to a variable and access each field separately, or even Microbit.accel().x will work