What is the closest zoo to zhengzhou?

Well, as I know, the zoo in ZZ has already returned the panda back to Sichuan, so I am afraid that you cannot see the panda there.
However, you can head for Xi'an Qinling Wildlife Park to see the pandas. You can take the high speed train from East ZZ Railway Station to North Xi'an Railway Station. It only takes about 2.5 hours. Upon arrival, you can take metro line 2 from there to Hangtiancheng Station, Exit B. Then you may transfer bus no.320 or Tourist Bus Line 9 at the beside bus stop to Qinling Wildlife Park directly.