Can you take the trolley to the zoo from Canal street?

Yes

Yes and you can take the bus also the trolley makes a stop right in front of Audubon park/zoo

Take STREET CAR to Audubon Park (nice, about 2 street blocks long) walk thru park, and Zoo is there across Magazine Street.

Where is the street car pick up to take me to the zoo?

Yep!

Yes you can