If you will be able to design data structure and how objects will interact with each other in games such as (in the following order from the easiest one):
then you will have a base knowledge of how such things are done.
In fact you don't need to know DirectX or OpenGL at the beggining because in my opinion for a begginer there is way too much things to learn. Start with something simple. I would recommend SDL: http://lazyfoo.net/SDL_tutorials/index.php
I would suggest you to DON'T focus too much on platfom-specific libraries (like DirectX and Windows APIs) that are windows only and that will can change in any new windows version.
I would suggest you, instead, as someone suggested, to use a multi-platform library for developing your game (like SFML, SDL or OGRE3D). However seeing you are thinking to use this game in order to find a work as a programmer, perhaps the best thing is to follow what DeXecipher said before in this topic -> http://www.cplusplus.com/forum/general/95245/#msg511420
I am not a programmer, but the suggestion made by DeXecipher seems to me the one that offers you the most usefully hints about what-to-do to make a work that can increase your chances to find a specific employ.
DeXecipher did make some good points about designing your own game engine but the OP is not interested in doing that. He said he wants advice on what game engine to use and info on how to make his own game to put in his portfolio. VERY different things.
OP: Just Google your thread topic "how to make a game with C++" and start reading, looking at code, watch videos, etc. This question has been asked about a BILLION times. Your answers are literally all over the net.