DBA_DMT_USED_EXTENTS

All extents in the dictionary managed tablespaces

Columns
   ___________________________
 
   SEGMENT_FILEID
      File number of segment header of the extent
   SEGMENT_BLOCK
      Block number of segment header of the extent
   TABLESPACE_ID
      ID of the tablespace containing the extent
   EXTENT_ID
      Extent number in the segment
   FILEID
      File Number of the extent
   BLOCK
      Starting block number of the extent
   LENGTH
      Number of blocks in the extent

Related:

DBA_EXTENTS