I want to delete connections in tnsnames.ora. I need to figure out which ones are currently in use, so that I don't delete them mistakenly

> I'm using Oracle 12c in Debian 8 (on a vm) > > This question is for educational purposes only. I'm not using any production servers, so anything that you can tell me won't have consecuences To start with, I found this link to delete registers in tnsnames.ora. I didn't test it yet because first, I needed to know if there were active connections in the database using the information of the tnsnames.ora. I'm asking here because I found no way of doing this, but it may be possible to do it. For you to know, I'm using this command for connecting to the database, so that I clearly specify a tnsname

rlwrap sqlplus sys as sysdba@tnstest

The contents of my tnsnames.ora are the following

tnstest =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1539))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl)
    )
  )

But, if I want to be 100% sure that this is working, I use this command

tnsping tnstest

Which results are...

TNS Ping Utility for Linux: Version 12.2.0.1.0 - Production on 28-JAN-2020 23:51:38

Copyright (c) 1997, 2016, Oracle.  All rights reserved.

Used parameter files:
/opt/oracle/product/12.1.0.2/dbhome_1/network/admin/sqlnet.ora


Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1539))) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orcl)))
OK (0 msec)

After all of this I know that my configuration is working, I'm using a register in tnsnames.ora for the connection, but I don't know a way of checking... "Hey, now that I'm connected, I want to know which register I used from the tnsnames file for connecting, if I used that file of course" Is there any possibility that I could get this information? Well, my following attempts of trying to figure this out, were checking the v$session view, if there was any field that I could use to get this information, but I couldn't find one. After all of this, ultimately, I came here for asking. I don't know what else to try nor I have more ideas of what should I do next. > P.S: there's a chance that this problem is impossible to solve, because this is task I'm doing due to I'm a student of sysadmin, and our teacher intentionally added unsolvable questions. Even so, I still think there might be a solution for this particular case