Layover in PuDong Airport for 10 hrs. Would it be enough time to sightseeing around Shanghai ?

Generally, you can spare some time for sightseeing during transit. From T2, you can walk 10-15min to the Maglev train station to take Maglev to Longyang Road, where transfer to local subway line 2 to East Nanjing Road Station. Then you can walk to the Bund for sightseeing.

It is secure to check at the airport, but maybe a little bit busy. You are advised to spare at least 2h for check in.

Falicia, thank you very much:)
Moreover,
For visa, do I need to get any visa stamped even though I stay only 10 hrs outside of airport?
Can I use my credit card to buy train pass?

No visa is needed. Upon landing, you can easily apply for a transit permit from the frontier inspection, with which you are allowed to get out of the airport.

I remember it is ok to but the Maglev ticket with credit card, but for metro ticket, you have to pay with Chinese Yuan.