Hi Ritesh,
Extensibility Information about individual apps can be found by going to the Fiori Apps Library > All apps and searching for your app by name.
https://fioriappslibrary.hana.ondemand.com/sap/fix/externalViewer/#/detail/Apps('F1382')
On the Implementation Information tab you will find the Extensibility section and a link to Extensibility help in the SAP Library for that app.
For People Profile, the BADI to hide/amend the user interface sections is listed there along with all the relevant user interface section types including Notes.
P.S. SAP RIVER is no longer a name that is used. SAP Web IDE is the correct name for the recommended development environment for Fiori apps