Cannot get the << overload working and cannot print the 'Account' instance using 'getter' method through Node. Not entirely sure what additional information to provide, please just ask for anything else I didn't clarify!
There is very obviously something wrong with my operator overloading, but I'm not sure what it is.

Account.cpp
#include "Account.h"
namespace myNamespace{
   // CONSTRUCTOR
   Account::Account(int initialValue)
   {
       acct_balance = initialValue;
   }
   //MUTATOR MEMBER FUNCTION
   void Account::deposit(int amount)
   {
       acct_balance += amount;
   }


   void Account::withdraw(int amount)
   {
       acct_balance -= amount;
   }


   void Account::setName(std::string newName)
   {
      name = newName;
   }
   //QUERY MEMBER FUNCTION
   int Account::balance() const
   {
       return acct_balance;
   }


   bool Account::has_funds() const
   {
      return (acct_balance > 0.0);
   }


   std::string Account::getName()
   {
      return name;
   }


   int& operator += (Account& a,const Account& b)
   {
      a.acct_balance += b.balance();
      return a.acct_balance;
   }


   std::ostream& operator << (std::ostream& out, const Account& a)
   {
      out << a.acct_balance;
   }
};


main.cpp

#include <iostream>
#include <string>
#include "Account.h"
#include "Node.h"




using namespace myNamespace;
using namespace std;


int main()
{
   Node<int>* intNode = new Node<int>(5);
   Node<std::string>* stringNode = new Node<std::string>("hello");
   Account* acc1 = new Account();
   Node<Account>* accountNode = new Node<Account>(*acc1);
   


   cout << "Initialised intNode with " << (intNode)->getData() << " ,\n";
   cout << "Initialised stringNode with "    << stringNode->getData() << " ,\n";
   cout << "Intiialised accountNode with $" << accountNode << "." << endl;
   return 0;
}


/*
Modify the Node class you produced in the last few weeks so that it becomes
a class template for a Node that can store a pointer to a generic type
instance. The constructor for your new Node returns a pointer to the newlycreated
Node instance, which has been created in the heap. Instantiate a
Node to store a pointer to an int; a pointer to a string; and a pointer to
an Account.
*/


Node.h

#ifndef NODE_H
#define NODE_H
#include <iostream>
using namespace std;


namespace myNamespace{
{
   template <class T>
   class Node
   {
   public:
      Node(T const& initData, Node<T>* const& initPrev = NULL, Node<T>* const& initNext = NULL);
      void setData(T newData);
      T getData();
      void setPrev(Node<T>* newPrev);
      Node<T>* getPrev();
      void setNext(Node<T>* newNext);
      Node<T>* getNext();


      friend std::ostream& operator << (std::ostream& out, const Node<T>& a);
   private:
      T data;
      Node<T> *next;
      Node<T> *prev;
   };
   #include "Node.template"
}
#endif


Node.template

template <class T>
Node<T>::Node(T const& initData, Node<T>* const& initPrev, Node<T>* const& initNext)
{
   data = initData;
   prev = initPrev;
   next = initNext;
}


template <class T>
void Node<T>::setData(T newData)
{
   data = newData;
}


template <class T>
T Node<T>::getData()
{
   return data;
}


template <class T>
void Node<T>::setPrev(Node<T>* newPrev)
{
   prev = newPrev;
}


template <class T>
Node<T>* Node<T>::getPrev()
{
   return prev;
}


template <class T>
void Node<T>::setNext(Node<T>* newNext)
{
   next = newNext;
}


template <class T>
Node<T>* Node<T>::getNext()
{
   return next;
}


template <class T>
std::ostream& operator << (std::ostream& out, const Node<T>& a)
{
   out << a->getData();
}



When I print it out using


cout << "Initialised intNode with " << (intNode) << " ,\n";
cout << "Initialised stringNode with "    << (stringNode) << " ,\n";
cout << "Intiialised accountNode with $" << (accountNode) << "." << endl;


The output is
Initialised intNode with 0x7f9251c03950 ,
Initialised stringNode with 0x7f9251c03970 ,
Intiialised accountNode with $0x7f9251c039c0.


When dereferencing, here is the error



Undefined symbols for architecture x86_64:
  "myNamespace::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, myNamespace::Node<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > const&)", referenced from:
      _main in main.o
  "myNamespace::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, myNamespace::Node<myNamespace::Account> const&)", referenced from:
      _main in main.o
  "myNamespace::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, myNamespace::Node<int> const&)", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [runfile] Error 1

EDIT: IT'S SOLVED, EVERYBODY! Turns out the error was because I'm stupid! xP