Sometimes when you run datapump export, it might take a lot of time. Meanwhile client might ask you for the % of export completed. You can use below query to get the details of how much % export is done.

SELECT SID, SERIAL#, USERNAME, CONTEXT, SOFAR, TOTALWORK, ROUND(SOFAR/TOTALWORK*100,2) "%_COMPLETE" FROM V$SESSION_LONGOPS WHERE TOTALWORK != 0 AND SOFAR <> TOTALWORK;