Using TSM command line, in stgpool you can have detailed informations

tsm: TSM01>q stgpool CONTAINER1 f=d                              

                     Storage Pool Name: CONTAINER1
                     Storage Pool Type: Primary
                     Device Class Name: 
                          Storage Type: DIRECTORY
                            Cloud Type: 
                             Cloud URL: 
                        Cloud Identity: 
                        Cloud Location: 
                    Estimated Capacity: 8 188 G
                    Space Trigger Util: 
                              Pct Util: 65,3
                              Pct Migr: 
                           Pct Logical: 
...
       Maximum Scratch Volumes Allowed: 
        Number of Scratch Volumes Used: 
...
              Storage Pool Data Format: Native
...
                     Deduplicate Data?: Yes
  Processes For Identifying Duplicates: 
                            Compressed: Yes
   Additional space for protected data: 
            Total Unused Pending Space: 
                 Deduplication Savings: 21,905 G (68.86%)
                   Compression Savings: 4,560 G (46.03%)
                     Total Space Saved: 26,465 G (83.19%)

Using TSM database informations:

tsm: TSM01> select STGPOOL_NAME,POOLTYPE,DEVCLASS,NEXTSTGPOOL,DEDUPLICATE,EST_CAPACITY_MB,PCT_UTILIZED,PCT_LOGICAL,MAXSCRATCH,NUMSCRATCHUSED,DEDUP_SPACE_SAVED_MB,COMP_SPACE_SAVED_MB,SPACE_SAVED_MB from stgpools where stgpool_name='CONTAINER1'

        STGPOOL_NAME: CONTAINER1
            POOLTYPE: PRIMARY
            DEVCLASS: 
         NEXTSTGPOOL: 
         DEDUPLICATE: YES
          COMPRESSED: YES
     EST_CAPACITY_MB: 8384423.0
        PCT_UTILIZED: 65.3
         PCT_LOGICAL: 
          MAXSCRATCH: 
      NUMSCRATCHUSED: 
DEDUP_SPACE_SAVED_MB: 22374208
 COMP_SPACE_SAVED_MB: 4669518
      SPACE_SAVED_MB: 27043726

STOREDMB=($EST_CAPACITY_MB*$PCT_UTILIZED/100)
PCTDEDUP=(100*$SPACE_SAVED_MB/($SPACE_SAVED_MB+$STOREDMB))
RATIO=(($SPACE_SAVED_MB+$STOREDMB)/$STOREDMB)

Example:
STOREDMB=(8384423.0*65.3/100)=5475028 MB (5.22 TB)
PCTDEDUP=(100*27043726/(27043726+5475028))=83.16 %
RATIO=((27043726+5475028)/5475028)=5.93 (ratio: 5.9:1)

So you have a deduplication rate of 83% that means you will reduce the capacity of the data stored with 5.9:1, now you can also check the reduction related to compression and deduplication