meaning of const void * const pMem

The trick is to read from right to left :

        "pMem is a const pointer (*) to a const void"

So, it's a const pointer, meaning that the pointer itself cannot be modified.
And, it's pointing to const data, meaning that we cannot modify that data by using this pointer.

pMem is a constant pointer to a constant void

However, it might be best to take the void out, and consider something like this instead

const int * const p

Here, p is a constant pointer to a constant int - meaning that you cannot [should not ;-) ] alter the pointer's value, OR the value of the int pointed to.


So,

int n = 0;

const int * const p = &n;

You cannot do, for example, p++, or *p = 1;

>> const void * const pMem
It is a constant pointer to a constant type of void. The void pointer is a generic pointer type that can be set to point to any object. It is often used in C to allow the address of unknown objects to be passed to a function. For example, think of memcpy that uses this pointer type. In C++ it has very little use because (a) C++ focuses on things being type safe and (b) C++ has templates.

Let me try also an attempt (not cause any of the above comments was wrong or incomplete but to maybe set a different focus).

Let's first remove the const keywords (they have been explained excellently above). Then we have

  void * pMem;

That can be read in two ways:

(A)
It defines a pointer variable pointing to a void type

(B)
It defines a variable of  type void pointer.

The (A) often was used by C programmers (though not in the explanations above) and also by the C or C++ compiler. Here a pointer is just another way to access the 'real' data and there are little to no differences in the semantics using a pointer or a non-pointer. You often can recognize the (A) 'view' when the asterisk is placed directly at the variable and not at the type:

  void *pMem;

The (B) 'view' is favorite of most C++ programmers, but not only. If someone writes

   void* pMem;  

you can be sure that it is a (B) programmer ;-)

If you see  

   void * pMem;

(what is my current project style) it is indifferent (but probably a B).

But even in pure C you might find a statement like

typedef void *  VOIDPTR;

what is a obvious commitment to (B).

Here you can reade more about const declaration:
"The C++ 'const' Declaration: Why & How"
http://duramecho.com/ComputerInformation/WhyHowCppConst.html

May I ask why you gave a B grade ? That usually means that something was missing in the answer and/or that something is still unclear. If that's the case, then please do not hesitate to ask for clarification where needed.