If you walk in Central Park at the Scholar's Gate entrance (just off Central Park South) and walk the pathway toward the zoo. Walk past the restaurant (on your left) the ticket office (on your right) the zoo entrance (on your left). A bit past there, there is a place you can stand and see the sea lions.
If you enter via 65th Street (from 5th Ave, down the steps), it's in that general area. You really can't miss it.
If you come from the other end, you'll pass the Tisch Children's Zoo (petting zoo) on your left, past the Delacorte Clock (above you), and then walk a bit and the sea lions will be on your right.
Why not just go IN the zoo!?!?!? It only takes about an hour and a half to see everything (including the penguin and sea lion feedings). It's a GREAT little zoo!!! They have 3 gorgeous snow leopards; 2 adorable red pandas; 1 big polar bear; a bunch of cute little penguins; the Rain Forest, etc. .
I'm not sure how much tix are as I'm a member but whatever it is, it's totally worth it!