How would I go about getting the direction an entity is based upon the players current rotation yaw. Example: Say the player is looking North and the entity being tracked is behind the player, the direction would be south, and the same for all other directions. The direction would be entirely based upon where the entity is, and the players rotation yaw.

Do you want the direction to be in terms of pitch and yaw? if so, do you want them relative to the player's pitch and yaw or absolute?

Either way I suggest looking up ray tracing

Step 1: assume the player is at 0,0,0

Step 2: trigonometry