I am accessing SQLPLUS from a Server SRV01. My database D01 also resides on the same server. I need a TNS entry in that server so that my database is identified

When SQLPLUS and the database reside on the same server, you don't need a TNS entry. You can connect using the BEQ protocol (bequeath/local connection) with syntax like 'sqlplus / as sysdba' or 'sqlplus username/password'. The BEQ protocol uses inter-process communication directly without going through the network listener or TNS. TNS entries are only required for remote connections across the network. Local connections bypass the TNS layer entirely.