To get to the San Nicolás viewpoint, forget the car. You have two options: walking or taking the minibus of Granada urban transportation (line 31). Of course, if you go to Granada, this is one of the places you must visit, to behold the most beautiful view of the Alhambra.
You can take the bus at Plaza Nueva or Gran Vía de Colón, but apparently there are building works in the neighbourhood of Albaicín and the bus cannot stop at Plaza San Nicolás, so one has to get off at Iglesia San Salvador and the bus driver will give directions, above all to any foreigners traveling on the bus. I recommend taking a map of Granada so that you don't get lost, even though it is not too difficult to get there because there are various signs indicating the direction. I walked up there last time from Plaza Nueva (last year), with two friends from Granada, a beautiful walk, I highly recommend it if you have time. I descended walking both times, until arriving at Puerta Elvira.
Whatever way you choose, if it is at dusk, much better. You will enjoy a spectacular view of the Alhambra with the Sierra Nevada in the background.
Don't miss out on it.