which shuttle do I take to get to enterprise car rental at the SFO airport if arriving after 8pm?

Correct, there is no shuttle. You get the air train from the airport that does a loop to the other terminals, parking garage, and rental cars. There is a voiceover which informs you what is at each stop, as well as a map inside the air train

You'll have to take a air train ( i think that's what its called) to rentals and it enterprise will be on level 2 or 4 , i don't quite remember