sp_who

A new column, tempdbname, displays temporary database names of all active sessions.

 sp_who  fid spid status loginame origname hostname blk_spid dbname tempdbname
            cmd         block_xloid
  --- ---- -------- -------- -------- -------- -------- ------ ----------
         ----------------- -----------
    0    2 sleeping NULL   NULL     NULL            0 master tempdb
             DEADLOCK TUNE        0
    0    3 sleeping NULL   NULL     NULL            0 master tempdb
             SHUTDOWN HANDLER     0
    0    4 sleeping NULL   NULL     NULL            0 master tempdb
             ASTC HANDLER         0
    0    5 sleeping NULL   NULL     NULL            0 master tempdb
             CHECKPOINT SLEEP     0