Question

This prints an error message about qualifiers but don’t really understand what that means and how to adjust the code for it to work? Anyways, thanks a lot for looking at the code.

Note: The ostream operator is friended in the Node class.

using namespace std;

ostream& operator(ostream& output, const Node* currentNode)
{
   return output;
}

void Node::nodeFunction()
{
   //This node has items attached to the 'this' statement. After
   //the necessary functions, this is called to output the items.

   cout << this;
}

Answer 1

Your overloaded stream operator declaration should be like this:

std::ostream& operator<<(std::ostream& os, const T& obj);
^^^^^^^^^^^^^

You should be returning a reference to object of std::ostream, the & is wrongly placed in your overloaded function prototype.

Have a look at the working sample here.

Adding the source code here, for completeness.
Note: I have taken class Node members as public for ease of demonstration.

#include<iostream>

using namespace std;

class Node
{
    public: 
    int i;
    int j;
    void nodeFunction();

    friend ostream& operator <<(ostream& output, const Node* currentNode);     
};

ostream& operator<<(ostream& output, const Node* currentNode)
{
   output<< currentNode->i;
   output<< currentNode->j;

   return output;
}

void Node::nodeFunction()
{
   //This node has items attached to the 'this' statement. After
   //the necessary functions, this is called to output the items.

   cout << this;
}

int main()
{
    Node obj;
    obj.i = 10;
    obj.j = 20;

    obj.nodeFunction();

    return 0;
}