How do I know if my engine is locked on my QX56 Infiniti truck it won't start it's been one week and it just shut off while I was driving

To see if the engine is "locked", get a breaker bar and socket and put it on the crankshaft and manually turn the engine. A locked engine will not turn. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops