How can pointers container can have the ownership of pointers if pointers are already deleted?

In this code I tryed to make a template classP_array which store pointer to an object as shown below. simply the template class store pointers and delete them if not deleted after usage. so i should make NULL checking

Although this problem was addressed in other questions. I dont really understand how to check if pointer is NULL or not.

in the Destructor ~P_array() checking NULL pointers is not effective

I tryed something similar using std::share_ptr to explain the idea

p_array destructor:

~P_array() {
    unsigned int i = 0 ;
    while(i < total)
    {
        if (t_array[i])        //Not effective
        {
            std::cout << "deleting " << t_array[i] << "\n" ;
            delete (t_array[i]) ; //Ownership of pointer
        }
        i++;
    }
}    

main.cpp :

#include <iostream>
#include <memory>
#include "p_array.h"


class Obj {
    public: ~Obj () { std::cout << "Deleting Obj...\n" ;}
};


int main() {
    P_array<Obj> ap ;
    Obj * op[10] ;

    for (int i = 0; i < 10 ; i++)
    {
        op[i] = new (Obj) ;
        ap.add(op[i]);
    }

    //if (sp.get())  delete sp.get() ; // invalid pointer error
    sp.reset() ;

    //delete op[0] ;// gives double free error
}

So simply my question is:

1- If I delete a pointer which is stored in a container which delete the pointers in the destructor then how the container knows if these pointers are accually deleted?

2- Does deleting a pointer makes it a NULL pointer ?

3- if the container can't check for deleted pointers then how it can gain the ownership of these pointers such in case of P_array example

My thanks