taken from the unity answers:
You want to calculate the direction between the enemy and the player, get the forward vector of the enemy, and then use Vector3.Angle to calculate the angle.
Then you can check if the angle is less than whatever angle you want to be the enemy's field of vision (eg: a 20 degree cone, for instance), and if it is, then the player is in that enemy's field of vision.
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so in playmaker terms, use the vector3 operator, set up two vector 3 variables and set it to Angle. Get the players vector3 and if it is in that range you use "You can Store Magnitude in Get Axis Vector and use Float Compare on that..."
and that is another way to do it!
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I also found this vector3 compare that Julius created.
http://hutonggames.com/playmakerforum/index.php?topic=3058.0