I need diagram that shows how the door handle works. Someone tried to steal my truck and punched out the lock. Can not get into my truck. HELP

sure, cuts horn wire and alarm horn.
s.o.p. most thief.
im the poor sod fixes this damage../.
the valet key allows just that. drive car and park it no alarms.
but breaking any car is easy for any pro to avg, thief.
to steal items in car,,

are you saying owner left a key in car?
a key fact . LOL

Check childproof lock if you can open it from the inside, but usually the connection between the handle and the lock for the outside door handle breaks.
if you can't open the door using either inside or outside door handles, go to a locksmith, auto electrician or a Nissan dealer or risk severely damaging the interior door panelling trying to do this yourself...
Please get back to us with the solution you found worked as it may help someone else in the future, thanks.

remove inside panal and look inside door. should be clip holding lock in place.

have you tried putting the key in the door and locking and unlocking it several times?

Must be the internal door linkage has slipped off from the inside door handle. You will have to get the door panel removed to fix that linkage. This is all assuming it's a front passenger door you're having the problem with.
Rear doors have child safety locks built in that prevent the doors from opening from the inside, to keep the little ones from opening the rear doors accidentally and tumbling out. Those you can just slide a safety lever to allow it to be opened from the inside.

There is a nice video on this over on youtube. Shows the guy pulling off the plastic covers and removing the lock cylinder. You can buy a new one from a dealer, cost about 65.00 and you have to get it keyed, but I think you can buy a generic GM lock cylinder with a key from autozone or advance.

Note I have had an official saturn lock cylinder sitting at a Chevy dealer for a week now as they can not figure out how to key it. Nice to have your keys match the doors and trunk. If you go with a generic one your new ignition key will not match your doors and trunk.

it depends on the door handle. if the lock is a part of the handle you will need to get the whole assembly and all that would consist of is two screws and the small bars that are connected too the handle an door latch. if it is a seprate piece all it would consist of is a c clip an one small bar to the door lock. tools needed will be screw driver possible 10mm wrench. hopefully your window regulator isn't in the way. if so let the window down so that the two screws at the bottom on the track are visible. remove the two screws and carefully remove the window. remember that it is glass so use extreme caution.

the lock should come out of the handle. usually there is a clip holding it in. sounds like its broken and you will need another handle, a locksmith should be able to get another lock and make it fit your old key. The dealer is the only place to get a new handle from as far as I know.

The owner's manual for your Discovery clearly states that this is a design feature to keep you from locking the keys in the vehicle. The doors must be locked with either the remote keyless entry transmitter, or with the key itself.

take a punch to the center of the rivet where sticking out nock it threw then drill out with drill bit