The point (0,-1) (mod order) confuses me. Seems that 2*(0,-1)=(0,1) and (0,-1)+(x,y)=(-x,-y). Does it indicates that the order is always even whatever the base Group (to which the cordinates belong) is?

Than, what’s the order of jubjub if using bls12_381 in proving system?

I don’t understand your question, could you clarify?

Jubjub’s order is 2^3 * 6554484396890773809930967563523245729705921265872317281365359162392183254199

We’re usually working in the prime-order subgroup.

My question is whether the order is a prime or an even number, and I wondered the structure of the group

Thanks to your answer, this question is clear now.

The order of (0, -1) is 2, but that point is not in the subgroup that is used for key agreement. Twisted Edwards curves always have points of order 2 and 4.