GMC 2015 Sierra Denali Owner's Manual page 351

10-80 Vehicle Care
4. If the flat tire is on the front of
the vehicle (1500 models),
position the jack under the
bracket attached to the vehicle's
frame, behind the flat tire, as
shown.
Front Position 1500 Models Rear Position 1500 Models
Front Position All Other Models
If the flat tire is on the front of
the vehicle (all other models),
position the jack under the
vehicle, as shown.