Show free blocks in temp tablespace

select tablespace_name, segment_file, total_blocks, free_blocks, free_blocks / total_blocks * 100 "% Free" 
    from V$SORT_SEGMENT;

Example:

TABLESPACE_NAME                                      SEGMENT_FILE TOTAL_BLOCKS FREE_BLOCKS     % Free
---------------------------------------------------- ------------ ------------ ----------- ----------
TEMP                                                            0        84352       82176 97.4203338