Not sure what you're doing there but you have defined a vector of HashEntry and calling cout on HashEntry but your operator<< overload operates on Symbol instead.
The operator<< for class Symbol should look something like this
class Symbol {
private:
friend ostream& operator<<(ostream &os, const Symbol &s);
int type;
string data;
};
ostream& operator<<(ostream &os, const Symbol &s)
{
os << s.data << " : " << s.type;
return os;
}