Try
locate sqlldr
That should return something like
/u01/app/oracle/product/11.2.0/xe/bin/sqlldr
Edit your ~/.profile and add at the bottom
export ORACLE_HOME=/u01/app/oracle/product/11.2.0/xe
PATH="$PATH:$ORACLE_HOME/bin"
Then re-load your profile with source ~/.profile
(or log out and log back in), and you should be good to go.