it is out at the top right side as u face the camera it is outward it is a Tamron 150 -600 f5 lens
Big, heavy zoom = bent lens mount on the camera body. Holding the lens release button in and gripping the lens as close to the body as possible then apply as much turning force as you can in the removal direction you might be able to get it to come off. Putting pressure inward at the outward bend area may help.
Once off the mirror box will need to be inspected but unless the drop force was on the lens side or front its likely fine.
Mine was a 75-300 zoom, the FA hit on the pentaprism and rewind knob on concrete and bent the lens mount out 1/8 inch at the bottom center. Your friends is likely bent out 1/8 to 5/32 inch close to the lens mount retaining screw.
Once off it may reinstall and remove easier but the electrical contacts on the lens will likely not mate with the body and therefore not operate properly.
Edit: Looking at my D300 the lens mount screws are at 1 o'clock, 4 o'clock, 6 o'clock, 8 o'clock, and 11 o'clock.