What do you think Na'Vi dick looks like

I don’t know how close it really is to the original

but you can find a very similar image in an abandoned school in the film (about 31 minutes of the film)

you can assume that since they are similar to cats, then the penis may look similar. It may have something like spikes on the skin. or due to the fact that it is more humanoids, it may tend to smoothness and be more like bumps.