inventory.print();
The game class has a member variable called player which is a reference to a Player object. The Player object has a member variable called Inventory which is a reference to an Inventory object. So you can access the Player object via the player reference on the game class and the Inventory object via the Inventory reference on the Player object.
TLDR;
player.Inventory.print();
The Microsoft.Net standards specify:
Method names should use Pascal case, so the print method should be called Print(), not print().
Public member fields should use Pascal case (Inventory member on Player class).
Protected and Private member fields should use Camel case (player member on IMPAGame class).