Hi Prabhakar,
First check this blog for FTPS How to setup a FTPS connection in PI 7.10
Run the XPI InspectorMichal's PI tips: XPI inspector - help OSS and yourself using option 50 (XI Channel) and select you receiver channel run the scenario, you will see the list of certificates like below screen shot it will tell you which one is trusted which ones are not trusted, you can download the certificates from there and import into NWA trusted keystore.
You can check below blog but this is for HTTPS but it is similar.
Using XPI Inspector to troubleshoot HTTP SSL connections
Regards,
Praveen.