it would be
- 860GS2028-GS on NSE
- 860GOI2028 on BSE
For more details, checkout this topic How to buy bond from secondary market - #3 by cvs
However, i am surprised that nothing comes-up in Kite-search
upon searching specifically for the NSE symbol of this above bond… 
I generally search for the ISIN in rbi.org.in to get the details of the bond like…
[ Source ]