I found a solution
from omni.isaac.core.utils.nucleus import find_nucleus_server
from omni.isaac.core.utils.stage import add_reference_to_stage
import carb
def setup_scene(self):
world = World.instance()
result, nucleus_server = find_nucleus_server()
if result is False:
carb.log_error("Could not find nucleus server with /Isaac folder")
usd_path = nucleus_server + "/Isaac/Props/Mounts/ur10_mount.usd"
stand = add_reference_to_stage(usd_path=usd_path, prim_path="/World/Stand")