Can you give me guide on planning a one day trip from Shanghai to Nanjing?

You can take a bullet train to NJ from Shanghai Railway Station or Hongqiao Railway Station (1.5-2.5 hours). The first train is scheduled at 6:00.

You may plan the tirp this way: Great Massacre Memorial Hall- the mausoleum- Confucious Temple. Afterwards, take a bullet train back to Shanghai from the main railway station or South Railway Station. By the way, the last train departs from the Main Railway Station at 22:51, and the last train departs from South Railway Station at 22:14. Don't miss it. :)

Thanks so much, Bill. Really appreciated.

Btw which mausoleum are you referring to? Looks like a few of them in the city.

Also, do you recommend the Qinhuai River Cruise?

And which train station (Main or South) is easier to access to the places you mentioned.

Thanks
Bea

Hi, Bea! I mean Dr. Sun Yat-sen's Mausoleum.
Yes, Qinhuai River Cruise is also very good! You can also arrange your itinerary this way: Great Massacre Memorial Hall- Qinhuai River Cruise- Confucious Temple.
The main railway station is easier for you to access to these places.
I hope my advice will be helpful. Have a great time in the city! :)

Awesome! Thanks so much for your help, Bill. Very helpful info and tips!