You've hidden the class member variable console
in your constructor by declaring a local pointer with the same name. In other words, this:
QTextEdit* console = new QTextEdit(this);
should be this:
console = new QTextEdit(this);
As an alternative, consider using an initialization list:
gameClientInteraction::gameClientInteraction() : console(new QTextEdit(this))
{
// constructor code goes here
console->setGeometry(0,625,600,100);
console->setReadOnly(true);
console->append("Bienvenue !");
}