How can I use apple pencil 2 with ipad 8th generation

You can not. The 8th generation iPad is compatible with the first generation Apple Pencil.

You need the original, 1st gen Pencil with the chromed top cap and magnetic Lightning connector protective cap.

Both Pencils charge and pair differently.

You can't. You must use Apple Pencil 1. See the "Related Article" linked above for compatibility list.