You should find the queries in the following docs (link FND_USER with v$session).
How to Count Total Number of Users Connected to ORACLE Application (Doc ID 295206.1)
What is the Relationship Between the ICX_SESSIONS Table and the FND_LOGINS Table? (Doc ID 358823.1)
How To Find The IP Address Of The Client Machine From Where A Particular Forms User Is Connected ? (Doc ID 879092.1)
How to Track IP Address of the Form Session in Oracle application 11i (Doc ID 878931.1)