To know the object in the tablespace

select S.tablespace_name, s.owner, s.segment_name, s.segment_type,
sum(s.bytes) size_in_bytes,
round(sum(s.bytes) / 1024 / 1024, 2) size_in_m,
f.file_name
from sys.dba_segments s, sys.dba_data_files f
where f.tablespace_name = s.tablespace_name
and f.file_id = s.header_file
and s.tablespace_name in ('tablespace_name')
-- A good thing to check is for objects in the SYSTEM tablespace that have s.owner <> 'SYS'
group by s.tablespace_name, s.owner, s.segment_name, s.segment_type, f.file_name
Order by s.tablespace_name, s.owner, s.segment_name