For statspack at session level check spdoc.txt (8.1.7) section 4.5

Code:
4.5.  Specifying a Session Id

  If you would like to gather session statistics and wait events for a
  particular session (in addition to the instance statistics and wait events),
  it is possible to specify the session id in the call to Statspack.  The
  statistics gathered for the session will include session statistics,
  session events and lock activity.  The default behaviour is to not to
  gather session level statistics.

    SQL>  execute statspack.snap(i_session_id=>3);