You can get the details of locking from the following tables.

V$ACCESS
V$LOCK
V$LOCKED_OBJECT

You can even get the transaction details which has performed the lock.

You can kill the process from Oracle itself using the
SID, SERIAL# details from v$SESSION/v$PROCESS.

If you want to perform a OS level process termination then follow what SREDDY had adivced and terminate the process with the KILL command of the OS (UNIX), KILL -9 for a sure kill.

Cheers,
Nanda.